Unfortunately, AdMob for AppLovin supports only Rewarded Videos.
You need to provide payment information on all networks separately. AdMob mediates all networks but each ad network handle payments on their own.
Please attach log from your device when you try to load.
I don’t think so but you could try to test your game without plugin in TestFlight. Simply delete UMA from project, make distribution build, upload to TestFlight and check if it works. Please let me know what results are after this operation.