There are many problems that could affect this. When you start a domain transfer, you will need to make sure that Privacy Protection is turned off for the specific domain you'd like to transfer.
Sometimes the approval emails get stuck in the spam folders which could lead to them not being seen by the user.
And one final issue that could arise, the EPP code is out of date. EPP codes are a unique set of letters and numbers that prove that you are the owner of that domain. Once generated, these codes are valid for 40 days.
If you think any of these problems could affect your domain transfer feel free to submit a support ticket to us at any time.