If your client receives this message when trying to view their proposal / estimate you need to re-activate their client.
Find their client profile in your Clients list page, you can use the Inactive clients filter, and then start typing their name in the search field to find them
When you locate the client, open up their client window
From the Settings tab change their status to “Active”, or from the actions dropdown menu (the three dots ( … ) button), choose:
Change status
Then choose Active
Then you can resend the quote and the client should be able to see it by following the new link