The exp mod is very buggy due to server checks. When you send the amount you want you must be on the multiplayer search menu.
Lets say you are trying to mod social slayer pick the game mode > hover over start search > send exp amount > switch gamemodes to any other one then go back to social slayer start search. After you have done all that bs win the next game asap or end it in a tie. For some reason ties always work.
If you don't get it right the first game just keep sending the exp amount while searching for a new game if you reset the game you will also have to repeat the beginning process. If you need any more help with this just pm me.