How should I configure Netlify Functions to act as a Rest API backend only?

Hi @jkjokeebg

I suggest first having a read over the following feature request Support for creating RESTful APIs with Netlify Functions and also Can't call lambda function with DELETE or PUT methods (which links to https://netlifpress.netlify.app/) and Function rewrites based on HTTP method for REST API.

If you still have questions do not hesitate to reply here.