EPP code (or domain code) can be used to transfer a domain to another registrar. If you want to transfer a domain to another registrar, you can contact the NIC.UA support with the appropriate request and within 1-2 days your domain will be ready for transfer.
A EPP code is like a password to the domain: with it you or anyone else can transfer your domain from your account to any other registrar.
And what to do if your hosting provider, website development team, etc. asked for this code?
First of all, find out exactly what they need the EPP code for. After all, before you give up the "keys" to your property, it is better to clarify what they will do with them and how they can do it in another way.
If you order hosting, it is worth looking at the order form. Some hosting providers by default require EPP code to create hosting and domain transfer. Without any explanation that the domain transfer must be paid additionally, and the transfer itself takes 5+ days. And most importantly - that hosting does not need to transfer a domain at all to function!
Usually, if you use an external hosting (not in NIC.UA), you only need to set the necessary settings in the domain: and this setting you do in your dashboard and they immediately updated in the registry domain area. You do not need to wait 5 days.