Thank you for your answer.
By the your second part, I think you misunderstood what the client want a little.
The app itself is on the classic app store (google, apple), but the content is local (in the box). if the client is a museum for example, all the detail of the exposition are local. Like that, it can be change everytime an exposition change.
The popup page is done by dev and already finish. I provide systems expertise, in that case pfsense. my client DONT want authentification.
Like I say, I don't have all the technical detail but for the scenario would be (museum example) something like that:
Visitor come to museum, buy a ticket
Clerk sell ticket and say "You can have more info if you donwload the museum app"
Visitor connect to museum wifi
The popup pop up(?), with a link to the app stores (google or apple).
The user choose to download or not.
When he leave the front the front desk, he loose the wifi but the app with the museum info are in the phone so no 4G
The issue is with the popup which doesn't pop or block the user.
is it clearer? Frankly, I not sure I can do better because I don't have more information of the situation.
Still thank you again for the reply