POST/PUT Usage examples for BTT Server?

I am sending a text string to BTT server for set_string_variable, but am unable to get the API working for anything other than a simple URL like shown in the BTT server documentation. My server is local and not using https or authentication. Using HTTP Requests / Webserver · GitBook documentation:

open ""

How can I do this with POST or PUT? Guide says " Example Terminal Command (but you can call the URL however you like)" but no examples other than including the payload as part of the URL.

I have been trying for some time and can't figure out what the server wants for a POST or PUT.

The webserver is GET only, POST and PUT are not supported.