We have been asked to provide clarification on what your domain name is when you signup for a developer edition domain.
Congratulations for requesting a developer edition domain!
When you summited a request for a free developer edition domain, shortly after you should have received a welcome email with your credentials and domain information.
The welcome email provided with the URL to login to your domain. The URL includes the information to login directly in your domain.
For example a domain from the USA starts with https://skylight.upskill.io/login/ followed by dev-xxxx. Your domain name starts with the dev- and includes all the characters after the dev-.
For an EU domain the URL begins with https://skylight.eu.upskill.io/login followed by the same dev-xxx which is your domain name including the dev-.
If you have not received the welcome email please have a look at your spam folder as it could have inadvertently been placed there.