The EPP code, also known as an authorisation or auth code, is a secret and unique set of characters assigned by the domain registrar.
This code serves as a safeguard, along with other security measures (e.g., domain lock), ensuring that only the rightful owner can transfer a domain. If the wrong EPP code is provided when setting up a domain transfer, the transfer will not be completed.
There are some exceptions, such as .CO.UK or .EU domains, that use a different code. Similarly, some domain registrars require the EPP code to be unavailable through the user interface, so you may need to contact your domain provider and ask them to share the EPP code with you directly.