Hello, the cause might be that you haven't migrated your Minecraft account from
Mojang to
Microsoft
You can do this by following this
steps (click the word in blue).
If that doesn't work feel free to create a ticket on our
discord in the
#ticket-support channel, in the
ticket section where we can give you the assistance you may need and ask for screenshots if it's required to progress with the helping process.
I hope your issue gets sorted so you can join us on our server, if you've got any other questions you may ask on this thread or directly through my discord (
vanity#2347).
Best Wishes.
~Vanity / Lewis