What is the content-type (see the header) of the POST?

It looks like the apiKey value is inserted as key/value form data. My first hunch would be to pass the apiKey and other parameters like this:

Thanks @david_r​ for your reply! Find attached the response and request headers. I guess the request header is one of interest? The content-type I see there is: application/x-www-form-urlencoded

Furthermore, I should somewhere put the name of the zipfile to download in the HTTP caller. In general terms, do you have some advice how to derive from the browser console the necessary info to get a working HTTP request?

Somehow I only see your reply @david_r​  in the top right corner of my screen. The API documentation of this website is not that good. I tried the Telerik website, looks interesting, until now, no results in finding out what parameters I need.

Unfortunately these things can vary a lot between APIs and websites and there is no real standard on how to handle it, so it's almost impossible to give specific advice on a general basis. My recommandation would be to team up either with the IT support of the server in question, or with your local FME partner:

https://www.safe.com/partners/partner-locator/

Yeah, thats right! Thanks for your support anyway.