Prevent users from signing in to a public app?

[Surdusvacca]

Hi all,

One of my apps are made public. 
No user signin required.

About a month ago I shared the link to one of my colleagues.
When he installed appsheet, he also signed in (because he thought he had to), with his private Gmail.

Ofcouse appsheet then shortly after prompted me to buy more licens. I could do that, but in this specific case, the purpose is that no one has to sign in. 
How can I make sure they cannot sign in when the app is public? I find it a bit strange that it is possible to create an app as public, but if people do sign in without your knowledge, you're fined for it? - I mean, in theory. If people forwards the applink, it could be a hugh amount of license?

[AleksiAlkio]

When creating a public app, you should use Publisher Pro subscription. Is this app using it?

[Surdusvacca]

Okay, no it is not using Publisher Pro. 
I have core licenses. But this one app is going to be used in a public area. 
My colleague just asked (he is kind of owner of the product) if he could have this app on his phone as well.
And yeah, then the licens was pulled for him as well. I guess I just buy that extra license.

Maybe I misunderstood how 'Public app' works cause I still dont understand why I can set the app as 'No user signin required' and then just because he accidentally sign in, it pulls a license.

The reason why we have the option 'No user sign in required' is actually for the purpose of it expects people to buy the Publisher Pro subscription?

[AleksiAlkio]

When using the Core subscription you are not able to control your license amount. If someone shares the app link, who ever can open the app and then you will lost the control. When the app is in Publisher Pro, the license is per app and it doesn't matter how many users are using the app.