What is the API format to create a contact in Membership 2 pro?

I want to create a contact from an external site via API allowed through Membership 2 pro.

Please direct me to the document for this purpose or the format required for this API.

I would like to send a string request to create/update a contact via an API. I understand “Membership 2 Pro” has its own API that I could like to use for this purpose, but I don’t have any documentation to see the format and/or a sample request string.
Example of an api would be: https://api.site.com/request/update/id=1&firstname=John.

Please let me know where I can find this information or if you can send me the document.