Safe XP level method
(Patched) There's a new method but I won't be releasing it since I don't want it getting patched really fast.
1. Load up Outbreak on Zombies (Private Match).
2. On selection of your class, use the use method.
3. Complete the first main.
4. Once you completed first mission, it will ask you to head to the Anomaly to leave the world.
5. Once you arrive at the Anomaly. Enable Podium to leave world.
6. When the timer is counting down from "10 Seconds" Enable highest XP modifier via a trainer.
7. You must not kill during this process or you will be immediately banned! (you have been warned..).
8. Once you hit the loading screen to the next world. Put the XP scale back at 1. (default xp).
9. Enjoy your levels & repeat until your desire.
Edit: You can host for like 30 mins before getting banned with this method. Seems like they’re really trying to stop XP lobbies.
If anyone has a trainer with a working XP modifier, test this out on an alt since the game is free for a week and reply here if you got banned at all with this method.