Good day, hgpaintingsvcs!
There are two things to take note upon accepting the invitation link for your accountant. Let me discuss them with you so you can get your accountant added successfully to your QuickBooks Online account.
First, upon accepting the invitation link, your accountant will be asked for a user ID and a new password. This will be used upon logging in to QuickBooks online as your accountant.
A security key will be sent to the email used upon accepting the invitation link to verify the email.
Secondly, if your accountant accepts the link with an existing online account in QuickBooks, the password should match to the user ID. This is to verify that the login credentials are true and match with an online QuickBooks account.
You can check this article to learn more about the process: How to Sign Up for QuickBooks Online Accountant.
Please know that we're always here in the Community if you need some help.