It is possible to do this as I can't workout how based on the TRequest, TResponse definition. The below will obviously not compile.

Thanks

public class MyEndpoint : BaseEndpoint<PayloadBody, string>
...
[HttpPost("resource/{externalTicketId}")]
[Produces("application/json")]
[ProducesResponseType(StatusCodes.Status200OK, Type = typeof(string))]
public override ActionResult Handle([FromQuery] string externalTicketId, PayloadBody payload)
{
....