How to get recommendations via javascript fetch?

For getting recommendations, the documentation says, that I should send a GET request to
https://api.pipeless.io/v1/apps/123/algos/recommendations/content
with a JSON body. But Http does not allow a body for GET requests. When executing the example code, I get the following error:

Failed to execute 'fetch' on 'Window': Request with GET/HEAD method cannot have body.

What should I do? Could you just allow POST?