There can be many reasons, one of them is that the Developer Membership has expired. You need to gain access to the account in order to see what the problem is. Can you contact the person who setup the account?
You could also try to contact with Apple Developer Support (https://developer.apple.com/contact/#!/topic/select), but I think it's unlikely that they give you access to the account.
If you can't get access to the account, you can always create a new one and upload the app again.
tovkal
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Here is a sample project with the issue, in case somebody wants to try it: https://github.com/tovkal/PhotoSwift6