MC24 hasn't had any updates since March 2019. See Release Notes. JRiver doesn't keep updating MadVR for earlier versions that haven't had MC updates.
Maid is correct. If you are still using an older version, and want to get a newer version of MadVR you have to install it manually.
But why do you want a later version of MadVR maid? Must be something very specific. What version of MadVR and MC are you using now?