When you try and login to UEFN - Content Service
Can you login
If so look at this post where transfer of project takes place explained
Unable to transfer Fortnite Creative projects to a team without first opening them in UEFN. - General / Issues and Bug Reporting - Epic Developer Community Forums
You are adding yourself to the team and setting ALL permissions. You must be over 18 years old and have verified that status to works on teams management. All Team Members must be over 18 years. If you get a mother/father to join Fortnite then request to Epic Support that players between 13 to 18 be added to your Team.
If you do cheat on this age check you could get banned.
