doPost(e) does not return parameters but doGet(e) does?

Question

Nowhere on the internet is this specific problem or a fix for it mentioned, so here goes:

My app contains the following doGet() and doPost()

Answer 1

I think this is somewhat expected. When one does an HTTP GET the parameters are passed on the url. When it's a POST they go on the payload, not the url.

Try calling post like this (Apps Script code):

UrlFetchApp.fetch(scriptUrl, {method:'post', payload:'param1=value1¶m2=value2'});