I would like to use Google's AppMaker for G Suite to receive contact form submissions from my website.

Ideally the form would submit a POST request to AppMaker, but I haven't been able to find any way to POST data from an external service - only fetching. 

Is it possible to send data from a standard HTML form (NOT a Google Form) to an AppMaker endpoint, or is there a way to use Sheets as a Datasource and accomplish the same thing?