Can you read through this, and see if it applies to you? Short version is that if you get that error it means you’re trying to activated an already activated account.
If your email address includes the word frontier in it, I see that you have a Pro subscription that has not been assigned to you yet. Sign into this page:
https://ecom-prd.trimblepaas.com/ecom/portal#/subscription
choose Members, then in the SketchUp Pro panel look for the list of members. I think that it’s empty at the moment, and if you click the +Assign button and add yourself, you then will be able to sign in inside of SketchUp, and your subscription will work.
I do know of a current issue that might still affect you, so please let us know if you got further after assigning the subscription to yourself.