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.
At Hostinger, you can find the EPP code in the Domains section of your panel: How to Obtain the EPP or Auth Code for Domain Transfer at Hostinger 💡