Sending body/payload in a GET request may cause some existing implementations to reject the request — while not prohibited by the specification, the semantics are undefined. It is better to just avoid sending payloads in GET requests.

Requests using GET should only be used to request data (they shouldn't include data).

So before using GET with Body parameter, you must first ensure the servers are supporting it. It is possible that some servers might ignore the body of GET request or behavior like caching GET/HEAD requests might cause issues.

A payload within a GET request message has no defined semantics; sending a payload body on a GET request might cause some existing implementations to reject the request.

This API uses request body in GET requests. For a long time this was prohibited in RFC2616 HTTP specification, but since RFCs 7230-7237, it is only discouraged, since older implementations could reject such requests. However, given that major APIs such as ElasticSearch's already implement GET with request bodies, there is precedence to such implementation.