diff --git a/src/android/index.ts b/src/android/index.ts
index 9e58fc8a6..389a081b7 100644
--- a/src/android/index.ts
+++ b/src/android/index.ts
@@ -40,7 +40,10 @@ import {
   handleCoreApiRequest,
   CoreApiResponseSuccess,
   CoreApiResponse,
+  CoreApiEnvelope,
 } from "../walletCoreApiHandler";
+import { makeErrorDetails } from "../operations/errors";
+import { TalerErrorCode } from "../TalerErrorCode";
 
 // @ts-ignore: special built-in module
 //import akono = require("akono");
@@ -132,9 +135,18 @@ export class AndroidHttpLib implements HttpRequestLibrary {
   }
 }
 
-function sendAkonoMessage(m: string): void {
+function sendAkonoMessage(ev: CoreApiEnvelope): void {
   // @ts-ignore
-  globalThis.__akono_sendMessage(m);
+  const sendMessage = globalThis.__akono_sendMessage;
+  if (typeof sendMessage !== "function") {
+    const errMsg =
+      "FATAL: cannot install android wallet listener: akono functions missing";
+    console.error(errMsg);
+    throw new Error(errMsg);
+  }
+  const m = JSON.stringify(ev);
+  // @ts-ignore
+  sendMessage(m);
 }
 
 class AndroidWalletMessageHandler {
@@ -154,7 +166,6 @@ class AndroidWalletMessageHandler {
     const wrapResponse = (result: unknown): CoreApiResponseSuccess => {
       return {
         type: "response",
-        isError: false,
         id,
         operation,
         result,
@@ -164,9 +175,7 @@ class AndroidWalletMessageHandler {
       case "init": {
         this.walletArgs = {
           notifyHandler: async (notification: WalletNotification) => {
-            sendAkonoMessage(
-              JSON.stringify({ type: "notification", payload: notification }),
-            );
+            sendAkonoMessage({ type: "notification", payload: notification });
           },
           persistentStoragePath: args.persistentStoragePath,
           httpLib: this.httpLib,
@@ -232,14 +241,6 @@ class AndroidWalletMessageHandler {
 }
 
 export function installAndroidWalletListener(): void {
-  // @ts-ignore
-  const sendMessage: (m: string) => void = globalThis.__akono_sendMessage;
-  if (typeof sendMessage !== "function") {
-    const errMsg =
-      "FATAL: cannot install android wallet listener: akono functions missing";
-    console.error(errMsg);
-    throw new Error(errMsg);
-  }
   const handler = new AndroidWalletMessageHandler();
   const onMessage = async (msgStr: any): Promise<void> => {
     if (typeof msgStr !== "string") {
@@ -262,16 +263,19 @@ export function installAndroidWalletListener(): void {
       console.log(
         `android listener: sending success response for ${operation} (${id})`,
       );
-      sendMessage(JSON.stringify(respMsg));
+      sendAkonoMessage(respMsg);
     } catch (e) {
-      const respMsg = {
-        type: "response",
+      const respMsg: CoreApiResponse = {
+        type: "error",
         id,
         operation,
-        isError: true,
-        result: { message: e.toString() },
+        error: makeErrorDetails(
+          TalerErrorCode.WALLET_UNEXPECTED_EXCEPTION,
+          "unexpected exception",
+          {},
+        ),
       };
-      sendMessage(JSON.stringify(respMsg));
+      sendAkonoMessage(respMsg);
       return;
     }
   };
diff --git a/src/walletCoreApiHandler.ts b/src/walletCoreApiHandler.ts
index 02b916af7..a16490d5a 100644
--- a/src/walletCoreApiHandler.ts
+++ b/src/walletCoreApiHandler.ts
@@ -30,6 +30,7 @@ import {
   makeCodecOptional,
 } from "./util/codec";
 import { Amounts } from "./util/amounts";
+import { OperationErrorDetails } from "./types/walletTypes";
 
 interface AddExchangeRequest {
   exchangeBaseUrl: string;
@@ -156,10 +157,11 @@ async function dispatchRequestInternal(
   wallet: Wallet,
   operation: string,
   payload: unknown,
-): Promise<unknown> {
+): Promise<Record<string, any>> {
   switch (operation) {
     case "withdrawTestkudos":
-      return await withdrawTestBalance(wallet);
+      await withdrawTestBalance(wallet);
+      return {};
     case "getTransactions": {
       const req = codecForTransactionsRequest().decode(payload);
       return await wallet.getTransactions(req);
@@ -201,10 +203,11 @@ async function dispatchRequestInternal(
     }
     case "setExchangeTosAccepted": {
       const req = codecForAcceptExchangeTosRequest().decode(payload);
-      return await wallet.acceptExchangeTermsOfService(
+      await wallet.acceptExchangeTermsOfService(
         req.exchangeBaseUrl,
         req.etag,
       );
+      return {};
     }
     case "applyRefund": {
       const req = codecForApplyRefundRequest().decode(payload);
@@ -225,7 +228,8 @@ async function dispatchRequestInternal(
     }
     case "abortProposal": {
       const req = codecForAbortProposalRequest().decode(payload);
-      return await wallet.refuseProposal(req.proposalId);
+      await wallet.refuseProposal(req.proposalId);
+      return {};
     }
     case "retryPendingNow": {
       await wallet.runPending(true);
@@ -253,10 +257,18 @@ export type CoreApiResponse =
  | CoreApiResponseSuccess
  | CoreApiResponseError;
 
+export type CoreApiEnvelope =
+ | CoreApiResponse
+ | CoreApiNotification;
+
+export interface CoreApiNotification {
+  type: "notification";
+  payload: unknown;
+}
+
 export interface CoreApiResponseSuccess {
   // To distinguish the message from notifications
   type: "response";
-  isError: false,
   operation: string,
   id: string;
   result: unknown;
@@ -264,11 +276,10 @@ export interface CoreApiResponseSuccess {
 
 export interface CoreApiResponseError {
   // To distinguish the message from notifications
-  type: "response";
-  isError: true,
+  type: "error";
   operation: string,
   id: string;
-  error: unknown;
+  error: OperationErrorDetails;
 }
 
 /**
@@ -283,11 +294,10 @@ export async function handleCoreApiRequest(
   try {
     const result = await dispatchRequestInternal(w, operation, payload);
     return {
-      isError: false,
+      type: "response",
       operation,
       id,
       result,
-      type: "response",
     };
   } catch (e) {
     if (
@@ -295,15 +305,14 @@ export async function handleCoreApiRequest(
       e instanceof OperationFailedAndReportedError
     ) {
       return {
-        isError: true,
+        type: "error",
         operation,
         id,
         error: e.operationError,
-        type: "response",
       };
     } else {
       return {
-        isError: true,
+        type: "error",
         operation,
         id,
         error: makeErrorDetails(
@@ -311,7 +320,6 @@ export async function handleCoreApiRequest(
           `unexpected exception: ${e}`,
           {},
         ),
-        type: "response",
       };
     }
   }
diff --git a/tests/components/wallet.py b/tests/components/wallet.py
index cedae84e1..bfdbd9ba1 100644
--- a/tests/components/wallet.py
+++ b/tests/components/wallet.py
@@ -21,12 +21,9 @@ class Wallet:
             print(r)
         assert r.returncode == 0
         json_r = json.loads(r.stdout)
-        if json_r["isError"]:
-            print(r)
-        assert not json_r["isError"]
-        if "result" not in json_r:
-            # TODO should there not always be a "result"?
-            return None
+        if json_r["type"] != "response" or "result" not in json_r:
+            print(json_r)
+        assert json_r["type"] == "response"
         return json_r["result"]
 
     def testing_withdraw(self, amount, exchange_url, bank_url):