diff --git a/frontend/src/lib/api-client.ts b/frontend/src/lib/api-client.ts
index cef77e2..ef0d8e2 100644
--- a/frontend/src/lib/api-client.ts
+++ b/frontend/src/lib/api-client.ts
@@ -40,8 +40,10 @@ async function request<T = any>(method: string, url: string, body?: any, extraIn
     })
 
     if (!res.ok) {
+      // Read the body once to avoid "Body has already been consumed" errors on non-JSON responses
+      const rawBody = await res.text().catch(() => '')
       let details: any = undefined
-      try { details = await res.json() } catch { details = await res.text() }
+      try { details = rawBody ? JSON.parse(rawBody) : undefined } catch { details = rawBody }
       const status = res.status
       if (status === 401) throw makeError('Unauthorized', 'UNAUTHORIZED', status, details)
       if (status === 403) throw makeError('Forbidden', 'FORBIDDEN', status, details)
@@ -114,4 +116,3 @@ export const chatbotApi = {
     }).then(res => res.json())
   }
 }
-
diff --git a/frontend/src/lib/proxy-auth.ts b/frontend/src/lib/proxy-auth.ts
index bbf7109..3b65f23 100644
--- a/frontend/src/lib/proxy-auth.ts
+++ b/frontend/src/lib/proxy-auth.ts
@@ -19,8 +19,10 @@ export async function proxyRequest(path: string, init?: RequestInit): Promise<Re
 
 export async function handleProxyResponse<T = any>(response: Response, defaultMessage = 'Request failed'): Promise<T> {
   if (!response.ok) {
+    // Read the body once to avoid "Body has already been consumed" when the upstream returns HTML errors
+    const rawBody = await response.text().catch(() => '')
     let details: any
-    try { details = await response.json() } catch { details = await response.text() }
+    try { details = rawBody ? JSON.parse(rawBody) : undefined } catch { details = rawBody }
     throw new Error(typeof details === 'string' ? `${defaultMessage}: ${details}` : (details?.error || defaultMessage))
   }
   const contentType = response.headers.get('content-type') || ''
@@ -28,4 +30,3 @@ export async function handleProxyResponse<T = any>(response: Response, defaultMe
   // @ts-ignore allow non-json
   return (await response.text()) as T
 }
-