return_code 此字段是通信标识，非交易标识，交易是否成功需要查看result_code来判断

[shinvdu]

    public function isSuccessful()
    {
        $data = $this->getData();
        return isset($data['return_code']) && $data['return_code'] == 'SUCCESS';
    }

https://github.com/shinvdu/omnipay-wechatpay/blob/master/src/Message/BaseAbstractResponse.php#L23

没有做result_code判断。

建议改为

return (isset($data['return_code']) && $data['return_code'] == 'SUCCESS' && isset($data['result_code']) && $data['result_code'] == 'SUCCESS');