diff --git a/app/src/lib/api/client.ts b/app/src/lib/api/client.ts
index 036af3df..98f98182 100644
--- a/app/src/lib/api/client.ts
+++ b/app/src/lib/api/client.ts
@@ -35,6 +35,21 @@ import type {
   WhisperModelSize,
 } from './types';
 
+function formatErrorDetail(detail: unknown, fallback: string): string {
+  if (typeof detail === 'string') return detail;
+  if (Array.isArray(detail)) {
+    return detail
+      .map((e: Record<string, unknown>) => e.msg || e.message || JSON.stringify(e))
+      .join('; ');
+  }
+  if (detail && typeof detail === 'object') {
+    const obj = detail as Record<string, unknown>;
+    if (typeof obj.message === 'string') return obj.message;
+    return JSON.stringify(detail);
+  }
+  return fallback;
+}
+
 class ApiClient {
   private getBaseUrl(): string {
     const serverUrl = useServerStore.getState().serverUrl;
@@ -55,7 +70,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -114,7 +129,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -148,7 +163,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.blob();
@@ -168,7 +183,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -188,7 +203,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -258,7 +273,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.blob();
@@ -272,7 +287,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.blob();
@@ -298,7 +313,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -343,7 +358,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.json();
@@ -616,7 +631,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.blob();
@@ -713,7 +728,7 @@ class ApiClient {
       const error = await response.json().catch(() => ({
         detail: response.statusText,
       }));
-      throw new Error(error.detail || `HTTP error! status: ${response.status}`);
+      throw new Error(formatErrorDetail(error.detail, `HTTP error! status: ${response.status}`));
     }
 
     return response.blob();