Let's perform some troubleshooting steps to ensure your accountant receives their invitation, DutchFriend.
 

I recommend clearing your browser’s cache to remove any stored data that may be causing issues with QuickBooks Self-Employed (QBSE).

If the issue persists, you can utilize a different browser to check for compatibility and rule out browser-specific problems. After completing these steps, send an invite again to your accountant. 
 

For any further concerns or queries, I’ll always be available on this thread to help.