There’s disagreement on whether it is within the http spec (https://stackoverflow.com/questions/978061/http-get-with-req...), but you can also send a body with a GET request, and you wouldn’t be alone in that; Elastic uses it, too (https://www.elastic.co/guide/en/elasticsearch/reference/curr...)
something like: example.com?body=%7B%22hello%22%3A%22world%22%7D
it's wierd, but I've seen that a lot.