I have made some mockups in XD and shared them with users in my organization. Some users have no problem accessing the link while others do. I checked with our account managers and IT folks and they are not sure why it's not working for everyone. I added the users with the same permission level to a mockup and one can get in but the other cannot.
I have an enterprise coporate account for Adobe Creative Cloud and think it doesn't have a link limit.
If anyone has any suggestions, that would be great. I love XD and want to share my stuff with my customers.