Error submitting request when sharing with a non-customer email

[Kyle Ouellette]

For context, we currently have Customer Sharing set to the the "Customers can search for other customers within their organizations, or manually enter the email address of other customers within their project" option. However, as far as I'm aware, customers have no visibility into the other customers for a given project (this is what we'd want, I'm just confirming my understanding). The issue arises when a customer tries to share their issue with a non-customer email. The fact they can't do this is correct and fits our use case, however, the issue is with the error message the user receives. The user gets an error "We couldn't submit your request. Refresh the page and try again." which is very unhelpful in my opinion. 

Is there a way to produce a better error message that indicates the issue is trying to share with a non-customer email address? If not, have others run into this issue, and if so, how did you go about navigating it? I can't imagine the expectation is customers knowing who is a customer and who is not so I'm hoping there's a better approach that makes this more intuitive for our customers.