401 error while installing the addon

Hi, one of our customer tries to install our addon through marketplace. But, he got 401 error message. Whereas it was working fine for others.

We have logs on when users install our app and the latest one was on 24th.

Here is the addon, https://marketplace.atlassian.com/apps/1219006/crystal-gantt?hosting=cloud&tab=overview!
Attached a image of what the user tried. Error-InstallingAddon|690x453

I get a 404 (not 401) error when I try to install it.

This is expected behavior when installing by first time and when installing immediately using Try Again will resolve this issue. But, in this case user has said he gets 401 error, what’s the reason for this?

Why is that the expected behavior?