Documentation for Downlink from Mqtt client

I’ve been using an mqtt client for a while to send downlinks to my sensors, but I’ve noticed lately that the Gateway always sends at the same frequency, and I would like to be able to control the send frequency, or the mode ADR is enabled, but by adding the frequency in my json file, the server application does not take it into account. I have the impression that it is just the field “data” and “fport” which are taken into account…

there is my json data that is sent via mqtt to the application server :

{"frequency":"867300000","confirmed":false, "fPort":46,"data":"af////+AAAA="}

on API Application server :

there is any documentation that descripe all the element we can add on the mqtt message and how writ it on the good format ?