diff --git a/src/config/auth.js b/src/config/auth.js
index 1bc236d..8050e8c 100644
--- a/src/config/auth.js
+++ b/src/config/auth.js
@@ -317,10 +317,19 @@ export async function validateRestApiAccess(httpClient, authManager) {
       { path: '/feeds', name: 'Feeds' }
     ];
 
+    // Get baseURL from httpClient for OAuth signature generation
+    const baseURL = httpClient?.defaults?.baseURL;
+
+    if (!baseURL) {
+      throw new Error('httpClient baseURL is not configured');
+    }
+
     const results = [];
     for (const endpoint of endpoints) {
       try {
-        const headers = authManager.getAuthHeaders();
+        // Generate proper OAuth headers with full URL for signature
+        const fullUrl = `${baseURL}${endpoint.path}`;
+        const headers = authManager.getAuthHeaders('GET', fullUrl, { per_page: 1 });
         await httpClient.get(endpoint.path, {
           headers,
           params: { per_page: 1 }
diff --git a/src/tests/helpers.js b/src/tests/helpers.js
index 5465874..609fba2 100644
--- a/src/tests/helpers.js
+++ b/src/tests/helpers.js
@@ -179,6 +179,7 @@ export class MockHttpClient {
     this.requests = [];
     this.responses = new Map();
     this.defaultResponse = new MockResponse();
+    this.defaults = { baseURL: 'https://test.example.com' };
   }
 
   /**