payData.signData并不是和wx.requestCommonPayment的signData一样是json，而是pay-tabble内部自己转了，文档有误 https://developers.weixin.qq.com/miniprogram/dev/platform-capabilities/industry/B2b_Pay.html#%E4%B8%80%E3%80%81B2b%E6%8F%92%E4%BB%B6-%E6%94%AF%E4%BB%98%E7%BB%84%E4%BB%B6