Hi Eliot,
They both have paid phone licenses. There are 3 Zoom One Pros licenses on the account, 2 of which are assigned to the members. And 5 licenses for Zoom Phone US & Canada Unlimited Calling, of which 2 are assigned to them as well. If I give the license to my account, I can add myself as a member of the shared line group but doesn't work specifically with the 2 members I want to add.
hi ahmedsoliman,
please go to admin->phone system management -> users and let me know what zoom phone licenses are assigned to each of the members of the zoom phone shared line group.
in your earlier post, i think you said that Both members have a Licensed Zoom One Pro and Zoom Phone Basic. zoom phone basic will not work.
zoom one pro does not include zoom phone.

Plans & Pricing for Zoom One | Zoom
it is easy to mix up licenses assigned to zoom users versus licenses assigned to zoom phone users.
Did my response answer your question? If so, please don't forget to mark the reply as an accepted solution.
thanks, eliot