One issue with some SBCs is that you are required to have a loyalty bonus to complete it, this is only obtained when a player has played 10 games for your club or you have packed them.
There is a simple quick loyalty trick to get around this, here's how it's done.
How To Get Loyalty In FIFA 20 Ultimate Team
There are a few ways to get loyalty. The more elaborate way is to simply go into a Squad Battles game against the CPU and play 10 games, which can be done on beginner difficulty; playing this difficulty will mean the CPU never really tackle you and you barely have to pay attention. This will give you your loyalty bonus, coins for completing each match AND will result in a decent ranking for the squad battle leaderboards; leading to more coins and packs. However, this is a lengthy process, potentially lasting up to 3 hours.
If you're looking to do it much quicker, you can simply quit out of games; but you will be given a loss on your record. Not an issue, if you're not particularly bothered by your record.
There is a simple way to do it on both PS4 and Xbox One without effecting your record: