QB Issue Resolution:

It is really important to have the invite sent to the email you use in your qbo acct.  I use 2 emails.  If someone sends it to the wrong one, I cannot access.  It has to be the one you use to log in with (even if you don’t use the email address as your user name).  Log into your QBOA acct and open email settings.

Resolution for Issue 'Cannot accept an invitation' available: Yes (Solved).
Source: Intuit Community forum.

Cannot accept an invitation: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for email settings
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Error Recovery for email settings [Canada]
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