After about a month of no help from QuickBooks Online Support I started trying everything I could think of to be able to accept an invite as a user. I noticed my User ID e-mail did not match my E-mail address on my QBO account. Once I correct this so that both were the same I was able to accept the invite.
-Login and click your Initial icon at the top right
-Click Manage Your Intuit Account
-Click Sign-in & Activity
- Verify your User ID and E-mail address are the same.
