diff --git a/packages/anastasis-core/src/index.ts b/packages/anastasis-core/src/index.ts
index 542e7eafb..5896dc655 100644
--- a/packages/anastasis-core/src/index.ts
+++ b/packages/anastasis-core/src/index.ts
@@ -196,6 +196,7 @@ function getCountries(
 
 export async function getBackupStartState(): Promise<ReducerStateBackup> {
   return {
+    reducer_type: "backup",
     backup_state: BackupStates.ContinentSelecting,
     continents: getContinents({
       requireProvider: true,
@@ -205,6 +206,7 @@ export async function getBackupStartState(): Promise<ReducerStateBackup> {
 
 export async function getRecoveryStartState(): Promise<ReducerStateRecovery> {
   return {
+    reducer_type: "recovery",
     recovery_state: RecoveryStates.ContinentSelecting,
     continents: getContinents({
       requireProvider: true,
@@ -571,6 +573,7 @@ async function uploadSecret(
       const talerPayUri = resp.headers.get("Taler");
       if (!talerPayUri) {
         return {
+          reducer_type: "error",
           code: TalerErrorCode.ANASTASIS_REDUCER_BACKEND_FAILURE,
           hint: `payment requested, but no taler://pay URI given`,
         };
@@ -579,6 +582,7 @@ async function uploadSecret(
       const parsedUri = parsePayUri(talerPayUri);
       if (!parsedUri) {
         return {
+          reducer_type: "error",
           code: TalerErrorCode.ANASTASIS_REDUCER_BACKEND_FAILURE,
           hint: `payment requested, but no taler://pay URI given`,
         };
@@ -587,6 +591,7 @@ async function uploadSecret(
       continue;
     }
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_NETWORK_FAILED,
       hint: `could not upload truth (HTTP status ${resp.status})`,
     };
@@ -674,6 +679,7 @@ async function uploadSecret(
       const talerPayUri = resp.headers.get("Taler");
       if (!talerPayUri) {
         return {
+          reducer_type: "error",
           code: TalerErrorCode.ANASTASIS_REDUCER_BACKEND_FAILURE,
           hint: `payment requested, but no taler://pay URI given`,
         };
@@ -682,6 +688,7 @@ async function uploadSecret(
       const parsedUri = parsePayUri(talerPayUri);
       if (!parsedUri) {
         return {
+          reducer_type: "error",
           code: TalerErrorCode.ANASTASIS_REDUCER_BACKEND_FAILURE,
           hint: `payment requested, but no taler://pay URI given`,
         };
@@ -690,6 +697,7 @@ async function uploadSecret(
       continue;
     }
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_NETWORK_FAILED,
       hint: `could not upload policy (http status ${resp.status})`,
     };
@@ -734,13 +742,13 @@ async function downloadPolicy(
     throw Error("invalid state");
   }
   for (const prov of state.selected_version.providers) {
-    const pi = state.authentication_providers?.[prov.provider_url];
+    const pi = state.authentication_providers?.[prov.url];
     if (!pi || pi.status !== "ok") {
       continue;
     }
     const userId = await userIdentifierDerive(userAttributes, pi.salt);
     const acctKeypair = accountKeypairDerive(userId);
-    const reqUrl = new URL(`policy/${acctKeypair.pub}`, prov.provider_url);
+    const reqUrl = new URL(`policy/${acctKeypair.pub}`, prov.url);
     reqUrl.searchParams.set("version", `${prov.version}`);
     const resp = await fetch(reqUrl.href);
     if (resp.status !== 200) {
@@ -759,7 +767,7 @@ async function downloadPolicy(
       policyVersion = Number(resp.headers.get("Anastasis-Version") ?? "0");
     } catch (e) {}
     foundRecoveryInfo = {
-      provider_url: prov.provider_url,
+      provider_url: prov.url,
       secret_name: rd.secret_name ?? "<unknown>",
       version: policyVersion,
     };
@@ -768,6 +776,7 @@ async function downloadPolicy(
   }
   if (!foundRecoveryInfo || !recoveryDoc) {
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_POLICY_LOOKUP_FAILED,
       hint: "No backups found at any provider for your identity information.",
     };
@@ -874,7 +883,7 @@ async function pollChallenges(
       const s2 = await requestTruth(state, truth, {
         pin: feedback.answer_code,
       });
-      if (s2.recovery_state) {
+      if (s2.reducer_type === "recovery") {
         state = s2;
       }
     }
@@ -1001,6 +1010,7 @@ async function requestTruth(
   }
 
   return {
+    reducer_type: "error",
     code: TalerErrorCode.ANASTASIS_TRUTH_CHALLENGE_FAILED,
     hint: "got unexpected /truth/ response status",
     http_status: resp.status,
@@ -1110,6 +1120,7 @@ async function selectChallenge(
   // FIXME: look at response, include in challenge_feedback!
 
   return {
+    reducer_type: "error",
     code: TalerErrorCode.ANASTASIS_TRUTH_CHALLENGE_FAILED,
     hint: "got unexpected /truth/.../challenge response status",
     http_status: resp.status,
@@ -1125,6 +1136,7 @@ async function backupSelectContinent(
   });
   if (countries.length <= 0) {
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_INPUT_INVALID,
       hint: "continent not found",
     };
@@ -1423,10 +1435,14 @@ async function nextFromChallengeSelecting(
   args: void,
 ): Promise<ReducerStateRecovery | ReducerStateError> {
   const s2 = await tryRecoverSecret(state);
-  if (s2.recovery_state === RecoveryStates.RecoveryFinished) {
+  if (
+    s2.reducer_type === "recovery" &&
+    s2.recovery_state === RecoveryStates.RecoveryFinished
+  ) {
     return s2;
   }
   return {
+    reducer_type: "error",
     code: TalerErrorCode.ANASTASIS_REDUCER_ACTION_INVALID,
     hint: "Not enough challenges solved",
   };
@@ -1462,7 +1478,7 @@ export function mergeDiscoveryAggregate(
     const oldIndex = polHashToIndex[pol.policy_hash];
     if (oldIndex != null) {
       aggregatedPolicies[oldIndex].providers.push({
-        provider_url: pol.provider_url,
+        url: pol.provider_url,
         version: pol.version,
       });
     } else {
@@ -1471,7 +1487,7 @@ export function mergeDiscoveryAggregate(
         policy_hash: pol.policy_hash,
         providers: [
           {
-            provider_url: pol.provider_url,
+            url: pol.provider_url,
             version: pol.version,
           },
         ],
@@ -1592,7 +1608,7 @@ const recoveryTransitions: Record<
     ...transition("add_provider", codecForAny(), addProviderRecovery),
     ...transition("delete_provider", codecForAny(), deleteProviderRecovery),
     ...transition(
-      "change_version",
+      "select_version",
       codecForActionArgsChangeVersion(),
       changeVersion,
     ),
@@ -1621,7 +1637,7 @@ export async function discoverPolicies(
   state: ReducerState,
   cursor?: DiscoveryCursor,
 ): Promise<DiscoveryResult> {
-  if (!state.recovery_state) {
+  if (state.reducer_type !== "recovery") {
     throw Error("can only discover providers in recovery state");
   }
 
@@ -1685,12 +1701,14 @@ export async function reduceAction(
     h = recoveryTransitions[state.recovery_state][action];
   } else {
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_ACTION_INVALID,
       hint: `Invalid state (needs backup_state or recovery_state)`,
     };
   }
   if (!h) {
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_ACTION_INVALID,
       hint: `Unsupported action '${action}' in state '${stateName}'`,
     };
@@ -1700,9 +1718,10 @@ export async function reduceAction(
     parsedArgs = h.argCodec.decode(args);
   } catch (e: any) {
     return {
+      reducer_type: "error",
       code: TalerErrorCode.ANASTASIS_REDUCER_INPUT_INVALID,
       hint: "argument validation failed",
-      message: e.toString(),
+      detail: e.toString(),
     };
   }
   try {
@@ -1710,7 +1729,10 @@ export async function reduceAction(
   } catch (e) {
     logger.error("action handler failed");
     if (e instanceof ReducerError) {
-      return e.errorJson;
+      return {
+        reducer_type: "error",
+        ...e.errorJson,
+      }
     }
     throw e;
   }
diff --git a/packages/anastasis-core/src/reducer-types.ts b/packages/anastasis-core/src/reducer-types.ts
index 7e8d4da25..03b40e4bd 100644
--- a/packages/anastasis-core/src/reducer-types.ts
+++ b/packages/anastasis-core/src/reducer-types.ts
@@ -73,19 +73,30 @@ export interface CoreSecret {
 }
 
 export interface ReducerStateBackup {
-  recovery_state?: undefined;
+  reducer_type: "backup";
+
   backup_state: BackupStates;
-  code?: undefined;
+
   currencies?: string[];
+
   continents?: ContinentInfo[];
+
   countries?: CountryInfo[];
+
   identity_attributes?: { [n: string]: string };
+
   authentication_providers?: { [url: string]: AuthenticationProviderStatus };
+
   authentication_methods?: AuthMethod[];
+
   required_attributes?: UserAttributeSpec[];
+
   selected_continent?: string;
+
   selected_country?: string;
+
   secret_name?: string;
+
   policies?: Policy[];
 
   recovery_data?: {
@@ -179,18 +190,10 @@ export interface RecoveryInformation {
 }
 
 export interface ReducerStateRecovery {
+  reducer_type: "recovery";
+
   recovery_state: RecoveryStates;
 
-  /**
-   * Unused in the recovery states.
-   */
-  backup_state?: undefined;
-
-  /**
-   * Unused in the recovery states.
-   */
-  code?: undefined;
-
   identity_attributes?: { [n: string]: string };
 
   continents?: ContinentInfo[];
@@ -267,11 +270,10 @@ export interface TruthMetaData {
 }
 
 export interface ReducerStateError {
-  backup_state?: undefined;
-  recovery_state?: undefined;
+  reducer_type: "error";
   code: number;
   hint?: string;
-  message?: string;
+  detail?: string;
 }
 
 export enum BackupStates {
@@ -302,12 +304,13 @@ export interface MethodSpec {
   usage_fee: string;
 }
 
-export type AuthenticationProviderStatusEmpty = {
+export type AuthenticationProviderStatusNotContacted = {
   status: "not-contacted";
 };
 
 export interface AuthenticationProviderStatusOk {
   status: "ok";
+
   annual_fee: string;
   business_name: string;
   currency: string;
@@ -320,8 +323,13 @@ export interface AuthenticationProviderStatusOk {
   // FIXME: add timestamp?
 }
 
+export interface AuthenticationProviderStatusDisabled {
+  status: "disabled";
+}
+
 export interface AuthenticationProviderStatusError {
   status: "error";
+
   http_status?: number;
   code: number;
   hint?: string;
@@ -329,7 +337,8 @@ export interface AuthenticationProviderStatusError {
 }
 
 export type AuthenticationProviderStatus =
-  | AuthenticationProviderStatusEmpty
+  | AuthenticationProviderStatusNotContacted
+  | AuthenticationProviderStatusDisabled
   | AuthenticationProviderStatusError
   | AuthenticationProviderStatusOk;
 
@@ -486,7 +495,6 @@ export interface PolicyMetaInfo {
   secret_name?: string;
 }
 
-
 /**
  * Aggregated / de-duplicated policy meta info.
  */
@@ -495,7 +503,7 @@ export interface AggregatedPolicyMetaInfo {
   policy_hash: string;
   attribute_mask: number;
   providers: {
-    provider_url: string;
+    url: string;
     version: number;
   }[];
 }
diff --git a/packages/anastasis-webui/src/pages/home/AttributeEntryScreen.tsx b/packages/anastasis-webui/src/pages/home/AttributeEntryScreen.tsx
index c14365d24..501415c40 100644
--- a/packages/anastasis-webui/src/pages/home/AttributeEntryScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/AttributeEntryScreen.tsx
@@ -19,7 +19,7 @@ export function AttributeEntryScreen(): VNode {
   const [attrs, setAttrs] = useState<Record<string, string>>(
     currentIdentityAttributes,
   );
-  const isBackup = state && state.backup_state;
+  const isBackup = state?.reducer_type === "backup";
   const [askUserIfSure, setAskUserIfSure] = useState(false);
 
   if (!reducer) {
diff --git a/packages/anastasis-webui/src/pages/home/AuthenticationEditorScreen.tsx b/packages/anastasis-webui/src/pages/home/AuthenticationEditorScreen.tsx
index 17987796f..f0cf9b88c 100644
--- a/packages/anastasis-webui/src/pages/home/AuthenticationEditorScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/AuthenticationEditorScreen.tsx
@@ -30,10 +30,7 @@ export function AuthenticationEditorScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
   const configuredAuthMethods: AuthMethod[] =
@@ -62,7 +59,7 @@ export function AuthenticationEditorScreen(): VNode {
   const authAvailableSet = new Set<string>();
   for (const provKey of Object.keys(providers)) {
     const p = providers[provKey];
-    if ("http_status" in p && !("error_code" in p) && p.methods) {
+    if (p.status === "ok") {
       for (const meth of p.methods) {
         authAvailableSet.add(meth.type);
       }
diff --git a/packages/anastasis-webui/src/pages/home/BackupFinishedScreen.tsx b/packages/anastasis-webui/src/pages/home/BackupFinishedScreen.tsx
index d6272d843..cbdfcdce7 100644
--- a/packages/anastasis-webui/src/pages/home/BackupFinishedScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/BackupFinishedScreen.tsx
@@ -9,10 +9,7 @@ export function BackupFinishedScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
   const details = reducer.currentReducerState.success_details;
diff --git a/packages/anastasis-webui/src/pages/home/ChallengeOverviewScreen.tsx b/packages/anastasis-webui/src/pages/home/ChallengeOverviewScreen.tsx
index f24478d19..11001194a 100644
--- a/packages/anastasis-webui/src/pages/home/ChallengeOverviewScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/ChallengeOverviewScreen.tsx
@@ -55,10 +55,7 @@ export function ChallengeOverviewScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "recovery") {
     return <div>invalid state</div>;
   }
 
diff --git a/packages/anastasis-webui/src/pages/home/ChallengePayingScreen.tsx b/packages/anastasis-webui/src/pages/home/ChallengePayingScreen.tsx
index ffcc8fafc..2e14f44cf 100644
--- a/packages/anastasis-webui/src/pages/home/ChallengePayingScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/ChallengePayingScreen.tsx
@@ -7,10 +7,7 @@ export function ChallengePayingScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "recovery") {
     return <div>invalid state</div>;
   }
   const payments = [""]; //reducer.currentReducerState.payments ??
diff --git a/packages/anastasis-webui/src/pages/home/EditPoliciesScreen.tsx b/packages/anastasis-webui/src/pages/home/EditPoliciesScreen.tsx
index 4e0dc2906..a57f7b08b 100644
--- a/packages/anastasis-webui/src/pages/home/EditPoliciesScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/EditPoliciesScreen.tsx
@@ -38,10 +38,7 @@ export function EditPoliciesScreen({
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
 
diff --git a/packages/anastasis-webui/src/pages/home/PoliciesPayingScreen.tsx b/packages/anastasis-webui/src/pages/home/PoliciesPayingScreen.tsx
index c3568b32d..2b2096dab 100644
--- a/packages/anastasis-webui/src/pages/home/PoliciesPayingScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/PoliciesPayingScreen.tsx
@@ -7,10 +7,7 @@ export function PoliciesPayingScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
   const payments = reducer.currentReducerState.policy_payment_requests ?? [];
diff --git a/packages/anastasis-webui/src/pages/home/RecoveryFinishedScreen.tsx b/packages/anastasis-webui/src/pages/home/RecoveryFinishedScreen.tsx
index d83482559..326a9a59d 100644
--- a/packages/anastasis-webui/src/pages/home/RecoveryFinishedScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/RecoveryFinishedScreen.tsx
@@ -18,10 +18,7 @@ export function RecoveryFinishedScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "recovery") {
     return <div>invalid state</div>;
   }
   const secretName = reducer.currentReducerState.recovery_document?.secret_name;
diff --git a/packages/anastasis-webui/src/pages/home/ReviewPoliciesScreen.tsx b/packages/anastasis-webui/src/pages/home/ReviewPoliciesScreen.tsx
index 4253f4617..5d75d5aaa 100644
--- a/packages/anastasis-webui/src/pages/home/ReviewPoliciesScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/ReviewPoliciesScreen.tsx
@@ -15,10 +15,7 @@ export function ReviewPoliciesScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
 
diff --git a/packages/anastasis-webui/src/pages/home/SecretEditorScreen.tsx b/packages/anastasis-webui/src/pages/home/SecretEditorScreen.tsx
index d9bf084ab..0931f4069 100644
--- a/packages/anastasis-webui/src/pages/home/SecretEditorScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/SecretEditorScreen.tsx
@@ -27,10 +27,7 @@ export function SecretEditorScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
 
diff --git a/packages/anastasis-webui/src/pages/home/SecretSelectionScreen.tsx b/packages/anastasis-webui/src/pages/home/SecretSelectionScreen.tsx
index 84f0303fe..45d8e46f3 100644
--- a/packages/anastasis-webui/src/pages/home/SecretSelectionScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/SecretSelectionScreen.tsx
@@ -31,7 +31,7 @@ export function SecretSelectionScreen(): VNode {
 
   if (
     !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
+    reducer.currentReducerState.reducer_type !== "recovery"
   ) {
     return <div>invalid state</div>;
   }
@@ -73,14 +73,17 @@ export function SecretSelectionScreen(): VNode {
   }
 
   return (
-    <AnastasisClientFrame title="Recovery: Select secret" hideNext="Please select version to recover">
+    <AnastasisClientFrame
+      title="Recovery: Select secret"
+      hideNext="Please select version to recover"
+    >
       <p>Found versions:</p>
       {policies.map((x) => (
         <div>
           {x.policy_hash} / {x.secret_name}
           <button
             onClick={async () => {
-              await reducer.transition("change_version", {
+              await reducer.transition("select_version", {
                 selection: x,
               });
             }}
@@ -119,7 +122,7 @@ export function OldSecretSelectionScreen(): VNode {
   }
   if (
     !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
+    reducer.currentReducerState.reducer_type !== "recovery"
   ) {
     return <div>invalid state</div>;
   }
@@ -127,7 +130,7 @@ export function OldSecretSelectionScreen(): VNode {
   async function doSelectVersion(p: string, n: number): Promise<void> {
     if (!reducer) return Promise.resolve();
     return reducer.runTransaction(async (tx) => {
-      await tx.transition("change_version", {
+      await tx.transition("select_version", {
         version: n,
         provider_url: p,
       });
diff --git a/packages/anastasis-webui/src/pages/home/SolveScreen.tsx b/packages/anastasis-webui/src/pages/home/SolveScreen.tsx
index c695b9b22..1070cf8a9 100644
--- a/packages/anastasis-webui/src/pages/home/SolveScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/SolveScreen.tsx
@@ -135,10 +135,7 @@ export function SolveScreen(): VNode {
       </AnastasisClientFrame>
     );
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.recovery_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "recovery") {
     return (
       <AnastasisClientFrame hideNav title="Recovery problem">
         <div>invalid state</div>
diff --git a/packages/anastasis-webui/src/pages/home/TruthsPayingScreen.tsx b/packages/anastasis-webui/src/pages/home/TruthsPayingScreen.tsx
index 6f95fa93b..c6f8cbead 100644
--- a/packages/anastasis-webui/src/pages/home/TruthsPayingScreen.tsx
+++ b/packages/anastasis-webui/src/pages/home/TruthsPayingScreen.tsx
@@ -7,10 +7,7 @@ export function TruthsPayingScreen(): VNode {
   if (!reducer) {
     return <div>no reducer in context</div>;
   }
-  if (
-    !reducer.currentReducerState ||
-    reducer.currentReducerState.backup_state === undefined
-  ) {
+  if (reducer.currentReducerState?.reducer_type !== "backup") {
     return <div>invalid state</div>;
   }
   const payments = reducer.currentReducerState.payments ?? [];