I would say you want to have a caching proxy set up on the delivery of all necessary content associated with downloading several popular LN wallets for the several platforms (iOS/Android/Mac/Linux/Windows).

Not really an easy way to get around the gating of the walled gardens on iOS, what's the deal with side loading on iOS anyway? Possible? You can always offer to help them with supervised initial full access to get on the App Store or whatever. Also, sideloading on Android might be a little problematic for some people, but it's usually just a popup asking if you want to enable "untrusted sources".

Or you could have it so that they are informed of a time limit and a platform-detecting page generates a link to click through to the platform download and then after 5 minutes of free access if they haven't paid they stop having their traffic forward over the link.

There also might be some way for you to "share" your "authorized" app installation package to your customers directly, again, I know jack diddly about apple, but that will be the most irritating problem you will encounter in all this.