Though indeed the integration allows you to specify any request method, even invalid ones:
…I wonder if it supports GET. Maybe it’s only supposed to support POST and PUT and maybe PATCH, so: any method that expects a request body?
Unless @johan can tell us more, I’d use POST rather than wasting time on GET. If you really want GET, then first test with https://requestb.in or FYI: TTN HTTP integration with 📩 Request Baskets instead of RequestBin.