One of the worries of businesses is that customers will change the app that's running on the phone or tablet. Luckily both Apple and Google thought of this and they have very simple ways to lock down what people can do.
iOS: https://support.apple.com/en-us/HT202612
Android: https://www.42gears.com/blog/android-equivalent-of-ios-guided-access-mode/
In addition to this you will probably want to make the application itself work like an native app, complete with icon and full-screen operation that works without the browser URL bars.
We have a post on how to do that here
