diff --git a/packages/taler-util/src/wallet-types.ts b/packages/taler-util/src/wallet-types.ts
index bc43652d9..2f9d3bb04 100644
--- a/packages/taler-util/src/wallet-types.ts
+++ b/packages/taler-util/src/wallet-types.ts
@@ -30,9 +30,11 @@
 import { AmountJson, codecForAmountString } from "./amounts.js";
 import { BackupRecovery } from "./backup-types.js";
 import {
+  Codec,
+  Context,
+  DecodingError,
   buildCodecForObject,
   buildCodecForUnion,
-  Codec,
   codecForAny,
   codecForBoolean,
   codecForConstString,
@@ -42,6 +44,7 @@ import {
   codecForNumber,
   codecForString,
   codecOptional,
+  renderContext,
 } from "./codec.js";
 import { VersionMatchResult } from "./libtool-version.js";
 import { PaytoUri } from "./payto.js";
@@ -50,40 +53,84 @@ import { TalerErrorCode } from "./taler-error-codes.js";
 import {
   AmountString,
   AuditorDenomSig,
-  codecForMerchantContractTerms,
-  codecForPeerContractTerms,
   CoinEnvelope,
-  DenominationPubKey,
   DenomKeyType,
+  DenominationPubKey,
   ExchangeAuditor,
   MerchantContractTerms,
   PeerContractTerms,
-  TrackTransaction,
   UnblindedSignature,
+  codecForMerchantContractTerms,
+  codecForPeerContractTerms,
 } from "./taler-types.js";
 import {
   AbsoluteTime,
-  codecForAbsoluteTime,
-  codecForTimestamp,
   TalerProtocolDuration,
   TalerProtocolTimestamp,
+  codecForAbsoluteTime,
+  codecForTimestamp,
 } from "./time.js";
-import {
-  codecForOrderShortInfo,
-  OrderShortInfo,
-} from "./transactions-types.js";
+import { OrderShortInfo } from "./transactions-types.js";
 
 /**
  * Identifier for a transaction in the wallet.
  */
-export type TransactionIdStr = `txn:${string}:${string}`;
+declare const __txId: unique symbol;
+export type TransactionIdStr = `txn:${string}:${string}` & { [__txId]: true };
 
 /**
  * Identifier for a pending task in the wallet.
  */
-export type PendingIdStr = `pnd:${string}:${string}`;
+declare const __pndId: unique symbol;
+export type PendingIdStr = `pnd:${string}:${string}` & { [__pndId]: true };
 
-export type TombstoneIdStr = `tmb:${string}:${string}`;
+declare const __tmbId: unique symbol;
+export type TombstoneIdStr = `tmb:${string}:${string}` & { [__tmbId]: true };
+
+function codecForTransactionIdStr(): Codec<TransactionIdStr> {
+  return {
+    decode(x: any, c?: Context): TransactionIdStr {
+      if (typeof x === "string" && x.startsWith("txn:")) {
+        return x as TransactionIdStr;
+      }
+      throw new DecodingError(
+        `expected string starting with "txn:" at ${renderContext(
+          c,
+        )} but got ${x}`,
+      );
+    },
+  };
+}
+
+function codecForPendingIdStr(): Codec<PendingIdStr> {
+  return {
+    decode(x: any, c?: Context): PendingIdStr {
+      if (typeof x === "string" && x.startsWith("txn:")) {
+        return x as PendingIdStr;
+      }
+      throw new DecodingError(
+        `expected string starting with "txn:" at ${renderContext(
+          c,
+        )} but got ${x}`,
+      );
+    },
+  };
+}
+
+function codecForTombstoneIdStr(): Codec<TombstoneIdStr> {
+  return {
+    decode(x: any, c?: Context): TombstoneIdStr {
+      if (typeof x === "string" && x.startsWith("tmb:")) {
+        return x as TombstoneIdStr;
+      }
+      throw new DecodingError(
+        `expected string starting with "tmb:" at ${renderContext(
+          c,
+        )} but got ${x}`,
+      );
+    },
+  };
+}
 
 /**
  * Response for the create reserve request to the wallet.
@@ -257,12 +304,12 @@ export enum ConfirmPayResultType {
 export interface ConfirmPayResultDone {
   type: ConfirmPayResultType.Done;
   contractTerms: MerchantContractTerms;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface ConfirmPayResultPending {
   type: ConfirmPayResultType.Pending;
-  transactionId: string;
+  transactionId: TransactionIdStr;
   lastError: TalerErrorDetail | undefined;
 }
 
@@ -279,14 +326,14 @@ export const codecForConfirmPayResultPending =
   (): Codec<ConfirmPayResultPending> =>
     buildCodecForObject<ConfirmPayResultPending>()
       .property("lastError", codecOptional(codecForTalerErrorDetail()))
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .property("type", codecForConstString(ConfirmPayResultType.Pending))
       .build("ConfirmPayResultPending");
 
 export const codecForConfirmPayResultDone = (): Codec<ConfirmPayResultDone> =>
   buildCodecForObject<ConfirmPayResultDone>()
     .property("type", codecForConstString(ConfirmPayResultType.Done))
-    .property("transactionId", codecForString())
+    .property("transactionId", codecForTransactionIdStr())
     .property("contractTerms", codecForMerchantContractTerms())
     .build("ConfirmPayResultDone");
 
@@ -387,7 +434,7 @@ export interface PrepareTipResult {
 }
 
 export interface AcceptTipResponse {
-  transactionId: string;
+  transactionId: TransactionIdStr;
   next_url?: string;
 }
 
@@ -419,7 +466,7 @@ export const codecForPreparePayResultPaymentPossible =
       .property("amountEffective", codecForAmountString())
       .property("amountRaw", codecForAmountString())
       .property("contractTerms", codecForMerchantContractTerms())
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .property("proposalId", codecForString())
       .property("contractTermsHash", codecForString())
       .property("talerUri", codecForString())
@@ -495,7 +542,7 @@ export const codecForPreparePayResultInsufficientBalance =
       .property("contractTerms", codecForAny())
       .property("talerUri", codecForString())
       .property("proposalId", codecForString())
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .property("noncePriv", codecForString())
       .property(
         "status",
@@ -520,7 +567,7 @@ export const codecForPreparePayResultAlreadyConfirmed =
       .property("talerUri", codecOptional(codecForString()))
       .property("contractTerms", codecForAny())
       .property("contractTermsHash", codecForString())
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .property("proposalId", codecForString())
       .build("PreparePayResultAlreadyConfirmed");
 
@@ -554,7 +601,7 @@ export type PreparePayResult =
  */
 export interface PreparePayResultPaymentPossible {
   status: PreparePayResultType.PaymentPossible;
-  transactionId: string;
+  transactionId: TransactionIdStr;
   /**
    * @deprecated use transactionId instead
    */
@@ -569,7 +616,7 @@ export interface PreparePayResultPaymentPossible {
 
 export interface PreparePayResultInsufficientBalance {
   status: PreparePayResultType.InsufficientBalance;
-  transactionId: string;
+  transactionId: TransactionIdStr;
   proposalId: string;
   contractTerms: MerchantContractTerms;
   amountRaw: string;
@@ -580,7 +627,7 @@ export interface PreparePayResultInsufficientBalance {
 
 export interface PreparePayResultAlreadyConfirmed {
   status: PreparePayResultType.AlreadyConfirmed;
-  transactionId: string;
+  transactionId: TransactionIdStr;
   contractTerms: MerchantContractTerms;
   paid: boolean;
   amountRaw: string;
@@ -603,7 +650,7 @@ export interface BankWithdrawDetails {
 export interface AcceptWithdrawalResponse {
   reservePub: string;
   confirmTransferUrl?: string;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 /**
@@ -1067,7 +1114,7 @@ export interface AcceptManualWithdrawalResult {
    */
   reservePub: string;
 
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface ManualWithdrawalDetails {
@@ -1362,12 +1409,12 @@ export const codecForAcceptExchangeTosRequest =
       .build("AcceptExchangeTosRequest");
 
 export interface AcceptRefundRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForApplyRefundRequest = (): Codec<AcceptRefundRequest> =>
   buildCodecForObject<AcceptRefundRequest>()
-    .property("transactionId", codecForString())
+    .property("transactionId", codecForTransactionIdStr())
     .build("AcceptRefundRequest");
 
 export interface ApplyRefundFromPurchaseIdRequest {
@@ -1615,7 +1662,7 @@ export interface PrepareRefundRequest {
 }
 
 export interface StartRefundQueryForUriResponse {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForPrepareRefundRequest = (): Codec<PrepareRefundRequest> =>
@@ -1624,13 +1671,13 @@ export const codecForPrepareRefundRequest = (): Codec<PrepareRefundRequest> =>
     .build("PrepareRefundRequest");
 
 export interface StartRefundQueryRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForStartRefundQueryRequest =
   (): Codec<StartRefundQueryRequest> =>
     buildCodecForObject<StartRefundQueryRequest>()
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .build("StartRefundQueryRequest");
 
 export interface PrepareTipRequest {
@@ -1639,7 +1686,7 @@ export interface PrepareTipRequest {
 
 export const codecForPrepareTipRequest = (): Codec<PrepareTipRequest> =>
   buildCodecForObject<PrepareTipRequest>()
-    .property("talerTipUri", codecForString())
+    .property("talerTipUri", codecForTransactionIdStr())
     .build("PrepareTipRequest");
 
 export interface AcceptTipRequest {
@@ -1652,35 +1699,35 @@ export const codecForAcceptTipRequest = (): Codec<AcceptTipRequest> =>
     .build("AcceptTipRequest");
 
 export interface SuspendTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForSuspendTransaction =
   (): Codec<SuspendTransactionRequest> =>
     buildCodecForObject<AbortTransactionRequest>()
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .build("SuspendTransactionRequest");
 
 export interface ResumeTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForResumeTransaction = (): Codec<ResumeTransactionRequest> =>
   buildCodecForObject<ResumeTransactionRequest>()
-    .property("transactionId", codecForString())
+    .property("transactionId", codecForTransactionIdStr())
     .build("ResumeTransactionRequest");
 
 export interface AbortTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface CancelAbortingTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForAbortTransaction = (): Codec<AbortTransactionRequest> =>
   buildCodecForObject<AbortTransactionRequest>()
-    .property("transactionId", codecForString())
+    .property("transactionId", codecForTransactionIdStr())
     .build("AbortTransactionRequest");
 
 export interface DepositGroupFees {
@@ -1727,11 +1774,11 @@ export const codecForCreateDepositGroupRequest =
 
 export interface CreateDepositGroupResponse {
   depositGroupId: string;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface TxIdResponse {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface WithdrawUriInfoResponse {
@@ -1762,23 +1809,23 @@ export interface WalletCurrencyInfo {
 }
 
 export interface DeleteTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface RetryTransactionRequest {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForDeleteTransactionRequest =
   (): Codec<DeleteTransactionRequest> =>
     buildCodecForObject<DeleteTransactionRequest>()
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .build("DeleteTransactionRequest");
 
 export const codecForRetryTransactionRequest =
   (): Codec<RetryTransactionRequest> =>
     buildCodecForObject<RetryTransactionRequest>()
-      .property("transactionId", codecForString())
+      .property("transactionId", codecForTransactionIdStr())
       .build("RetryTransactionRequest");
 
 export interface SetWalletDeviceIdRequest {
@@ -1907,12 +1954,12 @@ interface AttentionBackupUnpaid {
 
 interface AttentionMerchantRefund {
   type: AttentionType.MerchantRefund;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 interface AttentionKycWithdrawal {
   type: AttentionType.KycWithdrawal;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 interface AttentionExchangeTosChanged {
@@ -1942,12 +1989,12 @@ interface AttentionAuditorDenominationExpires {
 }
 interface AttentionPullPaymentPaid {
   type: AttentionType.PullPaymentPaid;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 interface AttentionPushPaymentReceived {
   type: AttentionType.PushPaymentReceived;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export type UserAttentionUnreadList = Array<{
@@ -2070,7 +2117,7 @@ export interface InitiatePeerPushDebitResponse {
   mergePriv: string;
   contractPriv: string;
   talerUri: string;
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForInitiatePeerPushDebitRequest =
@@ -2130,11 +2177,11 @@ export interface ConfirmPeerPushCreditRequest {
   peerPushPaymentIncomingId: string;
 }
 export interface AcceptPeerPushPaymentResponse {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export interface AcceptPeerPullPaymentResponse {
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 export const codecForConfirmPeerPushPaymentRequest =
@@ -2201,7 +2248,7 @@ export interface InitiatePeerPullCreditResponse {
    */
   talerUri: string;
 
-  transactionId: string;
+  transactionId: TransactionIdStr;
 }
 
 /**