Laravel Cashier Stripe API method calls is an optional per-request apiKey

I hope some one can help me, Im using Laravel 5.2 and Cashier 6, and Im getting this error

Api in RequestOptions.php line 77: The second argument to Stripe API method calls is an optional per-request apiKey, which must be a string, or per-request options, which must be an array. (HINT: you can set a global apiKey by "Stripe::setApiKey()")

but all the API of stripe are ok, thanks

via Chebli Mohamed