When using the Extranet app - Create Profile / Manage subscription for invitation for users (as it comes out of the box), the customer number is not populated for the new user. I've added the ExternalID as an extra field, and that field is set. The standard Swift template does have CustomerNumber included, but it looks like the code is not picking up the value and setting it to the new user.
<input type="hidden" name="UserManagement_Form_CustomerNumber" value="@Pageview.User.CustomerNumber">
Running latest 10.7
(Lars mentions this feature here: https://doc.dynamicweb.com/forum/ecommerce-standard-features/ecommerce-standard-features/importing-discounts)
Another issue with the invite modal is when an duplicate email is entered and the user clicks the invite button, the modal closes, and the error is shown on the page, but the modal with the data is now gone. I have been trying to keep the modal open to show the error there, but I'm guessing there are limitations in the system since the async post returns the full page.