The root cause is that self-hosted Teams have no customerId (Stripe ID). The migration copies it onto the Subscription, gets NULL, then deletes the Subscription. Run these before upgrading:
sqlUPDATE "Team" SET "customerId" = 'cus_selfhosted_' || id WHERE "customerId" IS NULL;
Then create Subscription records for any Teams missing them. If you've already attempted the upgrade and it failed, you'll also need to clean up 10 partially-created tables before retrying.
I ran into the same 20250522054050_add_organisations migration failure on a self-hosted Docker instance and spent some time digging into the root cause. The "fake subscription" workaround that's been floating around doesn't fully solve it — the issue goes deeper than a missing Subscription record.
I was able to fully resolve it and migrate from v1.8.1 → v2.6.0 with all 17 pending migrations applied and data intact. Posted details on the GitHub issue here: https://github.com/documenso/documenso/issues/1880
If anyone's still stuck on this and wants help getting unstuck, feel free to reach out.