A WeChat Pay REST API is an HTTP API designed in the RESTful style. All API requests must be HTTPS ones, and the message body of a request and response should be in the JSON format.
See Access Rules
https://apihk.mch.weixin.qq.com/hk/v3/transactions/app (Recommended for merchants outside China)
https://api.mch.weixin.qq.com/hk/v3/transactions/app (Recommended for merchants within China)
Note: A merchant can select a domain name which is most suitable for the merchant's request. Compatibility should be ensured. If an exception occurs when a domain name is accessed, another domain name can be used automatically.
WeChat Official Account Admin Platform:
After messaging between a follower and Official Accounts, the Official Accounts can get the follower's OpenID. Each user has a unique OpenID after its WeChat ID is encrypted. User's OpenID varies from different Official Accounts.
Official Accounts can get user's OpenID by the API below.
For information about user's alias, photo picture, gender, location, language, and following time, user's authorization is required.
URL: http://mp.weixin.qq.com/?lang=en_US
To use OpenIDs from different platforms as one ID for the same user, developers can use the API below:
URL: https://developers.weixin.qq.com/miniprogram/en/dev/
WeChat Open Platform:
Mobile apps can use the API below to get user's OpenID
Website apps can use the API below to get user's OpenID
Customer Service Tel
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WeChat Pay Global
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