问题描述： 请求 https://tp-pay.snssdk.com/gateway 这个接口一直报错 sign 错误 尝试了很久了 ，获取头条商户订单号。

报错截图、相关bug： {"response":{"code":"40001","msg":"Params Error","sub_code":"GW.SIGN_ERROR","sub_msg":"Sign Error"},"sign":"ao0UNbqEak66L8oT/WZigfpWGLs2XkNoCk6NlAaJxpSsWIrhWJUKEXJ8FNyIcGQ7cNbfojMP0weFRIJkCUvy5ilQhSxjwoIzLC2Ph37RSLFxx8paGczQNYOuNOIeazlIvqkHPqE3rVOslxQyZqWrzHzNLCbZ1KkD9pbOZV13eeg="}

复现步骤：

app_id=*********&biz_content={"out_order_no":"2019110510210156","uid":"*********","merchant_id":"*********","total_amount":1,"currency":"CNY","subject":"11","body":"111","trade_time":1572938359,"valid_time":"60","notify_url":"https:\/\/app.weidk.cn","risk_info":"{\"ip\":\"111.172.178.3\"}"}&charset=utf-8&format=json&method=tp.trade.create&sign=877592ac15bbe97cdc0cf981bef7659c&sign_type=MD5&timestamp=1572938359&version=1.0

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