I performed the account migration to the NA (North America) server.

After that my Tera wouldn't open on Steam, it shows an error message and I didn't want to play on the Game Forge launcher.



As my account had only one LVL 20 archer I decided to try a long shot.
I uninstalled the game and then still on my library screen I right-clicked Tera and went to manage> Remove from account.



Then I downloaded the game again and it started normally.
As I migrated the account from the old publisher to Game Forge and had not given any error screens, my content played on Steam was preserved.



Into the game I chose Server NA and when I went to the character selection screen, my archer was there, I believe that whoever had the whole set of items promised by Game Forge must have succeeded too.

This procedure worked for me. I don't guarantee it will solve your problem too, but good luck!