diff --git a/lib/services/pax8-client.ts b/lib/services/pax8-client.ts
index a796206..0885f0d 100644
--- a/lib/services/pax8-client.ts
+++ b/lib/services/pax8-client.ts
@@ -51,9 +51,16 @@ export class Pax8Client {
     }
 
     const data = await res.json();
+    // WR-03: a 200 response with an unexpected body shape (proxy/CDN error
+    // page reshaped as JSON, a future API version renaming the field, etc.)
+    // must not silently set accessToken to undefined and mask the failure
+    // behind a confusing 401 from the data endpoint later.
+    if (!data.access_token || typeof data.expires_in !== 'number') {
+      throw new Error('PAX8 token response missing access_token/expires_in');
+    }
     this.accessToken = data.access_token;
     this.tokenExpiry = Date.now() + data.expires_in * 1000;
-    return this.accessToken!;
+    return this.accessToken;
   }
 
   // Phase 11/12 will extend this with 429-aware Retry-After backoff for the