ok

app/Http/Middleware/CheckSign.php

@@ -15,7 +15,7 @@ class CheckSign
      */
     public function handle($request, Closure $next)
     {
-        $sign = $request->input('sign', '');
+        $sign = $request->post('sign', '');
         $key = 'a!A&AFRWT65Nb3NlklezUiqHyQAA@Z8M';
         $params = $request->except('_url');
         if ($sign == _sign($params, $key)) {