'Forced Update' for your App
The 'Forced Update' feature prompts users of your Purple App to update their app to your specified (minimum) version. This update is made mandatory in that way and will render the app unusable before it's performed, so the app update is unavoidable. Once you have submitted your new app version to the App Store with the 'Forced Update' setting enabled, a dialogue will appear on the user's device as the first screen when opening the app. The dialogue contains a (customisable) text and a link to the appropriate App Store to update to the latest app version.
The advantage of the forced update approach is that you can target even those of your app users who don't have automatic updates enabled on their devices in case you want to distribute a version of your app that should get used by all of your users, e.g. in case of an important security update.
Step 1 (optional): Learn in this article how to change the text of the 'Forced Update' dialogue