1, in the official document https://docs.open.alipay.com/62/104743 can be clearly seen in front of the bars plus input_charset not required, but is with a sample request. After that experiment, this must be added, otherwise it will return Alipay is busy.
2, the official document said: "MD5 signature merchants need to key value stitching behind the string" here because there is no example to cause a lot of people mistakenly think it is behind the increase in spliced or & & key = &&& ***. In fact, it is directly followed by the MD5 key, front do not have any character.