What an auth code (EPP code) is and why you need one

An auth code — also called an EPP code, transfer key or authorisation code — is a password that proves you're entitled to move a domain. The registry uses it to stop domains being transferred without the owner's consent.

Key points:

• Every gTLD domain has one. You get it from your current (losing) registrar, usually from their control panel or by request.
• It is case-sensitive and often contains special characters — copy and paste it rather than retyping.
• Some registrars email it to the registrant contact rather than showing it on screen, so make sure that email address works.
• Codes can expire or be regenerated; if a transfer rejects with an authInfo error, get a fresh code.

.uk domains don't use auth codes — they use an IPS tag change instead, so there's no code to fetch for a .co.uk. Some ccTLDs have their own variations, which the panel explains when you start the transfer.