Based on the screenshot you have entered it looks like the conflict is because your Region is set to Canada and the area code you are attempting to enter is in the U.S.
I would assume this is happening because your company account is a RingCentral Office Canada account. Because of this your region for the softphone is defaulted to Canada and cannot be changed to the U.S.
You will need to enter a Canadian area code to proceed. I would suggest choosing the Area Code of your main company number which I assume would be a Canadian number in this case. The region setting simply applies to a 7 digit dial. Any phone number in the same area code can be dialed by 7 digits instead of 10. That is the only functionality that this Region setting applies to.
Once you enter a Canadian Area Code you will be able to dial any phone number in the U.S. or Canada without issue as long as you dial using the 10 digit number.