Existing domain
When registering for the first time, there is a chance that your colleague or outsourced marketing, dev or SEO agency registered your domain already. When the domain was not verified yet, you will be able to successfully register for an already existing domain.
Limited access rights
However, access rights will be very limited and you won't see any monitoring data before taking necessary steps. The modal that will keep popping up looks as following:
This popup is explaining the next steps.
Verify registration
You should check your e-mail for a "Verify registration" mail and follow the steps. You will end up on a splash page that looks like the following:
This is the last step required. You will now have full access to the domain, and you will be able to downgrade rights of others, or even delete users. This can help to claim back a domain when it was accidentally or purposely hijacked.