diff --git a/lib/AuthHelper.php b/lib/AuthHelper.php
index e879964..617f542 100644
--- a/lib/AuthHelper.php
+++ b/lib/AuthHelper.php
@@ -170,6 +170,10 @@ public static function getAccessToken()
 
             $response = HttpRequestJson::post($config['AdminUrl'] . 'oauth/access_token', $data);
 
+            if (CurlRequest::$lastHttpCode >= 400) {
+                throw new SdkException("The shop is invalid or the authorization code has already been used.");
+            }
+
             return isset($response['access_token']) ? $response['access_token'] : null;
         } else {
             throw new SdkException("This request is not initiated from a valid shopify shop!");