diff --git a/src/Entity/ShippingGateway.php b/src/Entity/ShippingGateway.php
index 1b3b195..b2815b2 100644
--- a/src/Entity/ShippingGateway.php
+++ b/src/Entity/ShippingGateway.php
@@ -121,7 +121,7 @@ public function getConfigValue(string $key): ?string
             $key
         ));
 
-        return $this->config[$key];
+        return (string) $this->config[$key];
     }
 
     /**