Order number. There are the following three fields, which need to be generated according to the requirements of related algorithms. They are signature, order number (mch_billno) and random string. Wechat is a free application launched by Tencent on 20 1 1+2 1 to provide instant messaging service for intelligent terminals, which was created by the product team of Tencent Guangzhou R&D Center led by Zhang Xiaolong.