Check Subscription
Subscription plan must be Backer or higher.
Check Role
User role must be Administrator or Manager.
Navigate to Settings - Branding - Custom domain.
Click “Add data” option (edit icon) near Main APP row and input "Custom URL" for Main App, click "Add".
Click “Add data” option (edit icon) near Identity APP row and input "Custom URL" for Identity Server, click "Add".
Expand Rows for "Identity" and "Main App"
See Value, DNS type and Data - input all these information in your DNS settings.
Verify
Make sure you have inputed all data on your side, then click "Verify" buttonDone
If everything correct - system will update the statuses for Email row (Verified) and for nested rows (Authenticated). It may take some time.