External customer access creator app and connect wall

External customer access creator app and connect wall

I have an external customer set up to access a customer app via "creator customer add on" as part of one of our projects we have invited that customer to join our connect wall for a specific project so that they can see all the activity and provide input. When we invite them to the connect wall they get an error message saying the user already exists in org. We have checked everything and they only access via the portal. How can we get them external access to teh connect wall?
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