Update pay.js

[PascalSun]

fix 2 small issues:

• typo problem for duration
• the backend required field "fromUser", even though it doesn't be used in send message for this part, so we need add this field here for a quick fix

修复了两个问题：

• duration 打错了，少了个d
• 后端api要求必须有fromUser, 不然会报错，快速解决方式是在前端加一个fromUser的字段，这样后端就不会报400的错

[iamxjb]

谢谢