Most registrars will lock your domain automatically to protect you from unauthorized transfers. If you didn't contact your registrar or use your registrar's domain management tools to unlock your domain before you initiated your transfer, we won't be able to complete the transfer.
Generally if you see a message during the transfer that your domain is locked, you'll simply need to contact your registrar to unlock your domain.
In rare cases, a registrar may lock a domain for transferring while it resolves a billing or other dispute. If your registrar has actively locked your domain, you'll need to contact your registrar directly to resolve this issue and unlock your domain before you can complete your transfer.
Tip: Don't remember which registrar you used? Look it up.