I can't get Arcgis Pro trial, no error showing on username register pager. Has anybody tried and succeded in last month?
I assume you have used the ArcGIS trial account (not the public account).
Did you allocate the ArcGIS Pro license to the user using Manage Licenses in ArcGIS Online webpage after logging in using the administrative account (if you are the only user, you have the admin access)?
Configure licenses - ArcGIS Online