The EPP code, also known as an authorization or auth code, is a secret and unique set of characters assigned by the domain registrar.
This code is a safeguard that, along with other security measures (e.g., domain lock), guarantees 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.
The EPP key is required when transferring most TLDs, such as .COM, .NET, .ORG, .BIZ, .INFO, .US, etc.
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.