Hello Schlund,
Welcome to the Community! Thank you for choosing QuickBooks Online as your accounting software. Allow me to clarify things about inviting an accountant to access your company.
Signing up is free and lets them access all of the features available in your version of QuickBooks Online at no cost. However, your accountant's account should have the same version as yours.
The ability to work on your business using an account with a different region is unavailable. The contents, like the taxes and other features, will depend on it.
They can only add you as a client if they can create the account successfully and add a US phone number (see screenshot below).

Additionally, I want to share a link on how you can manage your accountants in QuickBooks. It contains information about inviting and removing accountants from an account: Add accountant users in QuickBooks Online.
Feel free to comment if you have more questions about the feature or need more clarification. We'll be around to help you through your thread. Have a great day.