As of Qlik Sense Enterprise on Windows September 2020, only GET and POST methods are supported in the REST connector.
That's limiting when using REST APIs out there, to say the least.
It should be possible to do a DELETE call to a REST API when needed, or a PUT or a DELETE or... you get the point.
Without these methods it's hard or impossible to create QSEoW-driven integrations with other systems.
I know, there's a possible workaround via using a http header "X-HTTP-Method-Override" to convince the API to use a specific http method, even if the call is coming in as a POST.
That's very much a hack though, and lots of REST APIs don't support that http header.
Please mark the post as a solution if it provided you with a solution to the topic at hand. Thanks!