文档地址：https://pay.weixin.qq.com/wiki/doc/api/wxpay_v2/papay/chapter3_3.shtml

委托代扣小程序纯签约，按照文档示例，打开新页面后提示：商家系统错误，请联系商家处理。支付中签约正常。

参数：

{
	plan_id: "170663",
	contract_code: "PC180158737568458342441520224655",
	request_serial: 1801587375684583425,
	contract_display_account: "test",
	notify_url: "https%3A%2F%2Fapi.example.com%2Fcallback%2F%2Fpayment%2Fcontract",
	timestamp: 1718366877,
	appid: "wx07caf209ad9c2f1d",
	mch_id: "1339046101",
	sign: "6DD98A538A8AEB76ECD7F39F44971536"
}