I have been successful in making Gaul as a playable faction. However, I can't for the life of me make them a faction that can migrate.

What I have tried:
edited everything in the factions table. I even used the Assembly Kit to enable the can_horde option.

Gave access to barbarian migration buildings from the building culture variants.

Edited the starting horde details and gave the Gaul leader his own horde buldings.

Nothing seems to work. The starting army just isn't in migration mode, and slowly suffers from attrition.

I have tried imitating other modders' work such as the Terminus Ageless Empires, where the Pontus faction was able to migrate as a Roman faction.

Any help is appreciated.