CS GO vote map with custom map list

I’m hosting my own casual server in CS GO by basically just inviting a bunch of friends into my lobby and starting a ‘practice with bots’ game. Not using sourcemod or any other fancy ways to start a server.
My question is how can I enable the ‘vote for next map’ feature and how do I modify the list of the maps that can be voted for?

I tried modifying gamemodes_server.txt and added my custom mapgroup, which I then included under the casual mapgroup. During the game, changed mp_endmatch_votenextmap to 1 from the console, but this didn’t help.