The roster vault does not work, and it has not worked since launch. It is a known bug. There is currently no way to use custom rosters in franchise mode.
SDS likely will claim that it is a “glitch” and that they will “work on fixing it” but it’s difficult to believe that SDS did not do this on purpose. Franchise is unplayable without being able to download the correct rosters. It forces people to play their micro transactions-laced diamond dynasty mode.

cubs1876_PSN
@cubs1876_PSN
Posts
-
-
Fix the roster vault. This is absolutely ridiculous. The game launched a week ago and it’s still impossible to start a franchise with the correct rosters. This is inexcusable
-
Yes. You can absolutely beat showdown using directional hitting. It helps if you never swing at the first pitch and take until you have 2 strikes.
Help: How to use Saved Roster in Franchise Mode?
Roster Vault
Showdowns - Directional Hitting