You CAN get into the AH but you have to do it a specific way:
1. Go to squads H2H and enter the menu for it (to where you can change your role)
2. From there go to view lineups, and to edit your lineup.
To buy:
3a. Select on a player to swap them, hover over an available player that is auctionable, and click to search auction instead, and you are in.
4.a Remove the position filter and search and buy away.
To sell:
3b. Insert into your lineup an un-upgraded player you wish to sell, go to upgrade them, and isntead post them to the auction house.