diff --git a/classes/core_jwt_manager.php b/classes/core_jwt_manager.php
index 0fd08ea..0e5544f 100644
--- a/classes/core_jwt_manager.php
+++ b/classes/core_jwt_manager.php
@@ -99,6 +99,7 @@ class core_jwt_manager
         try {
             $decoded = JWT::decode($keyvalue, new Key($secret, 'HS256'));
         } catch (\Exception $e) {
+            error_log('JWT decode error: ' . $e->getMessage());
             throw new \moodle_exception('invalidkey');
         }