: Go to Settings > Privacy & Security > Developer Mode and toggle it On (requires a device restart).
There are several reasons why you might want to use AltStore to install IPA files: how to install ipa file using altstore
Once AltStore is running on your phone and your computer is on the same Wi-Fi network with AltServer active: Download the IPA : Use Safari to download the desired file to your device. Open AltStore : Launch the AltStore app on your iPhone. Add the App tab at the bottom, then tap the in the top-left corner. Select the File : Browse your files and select the IPA you just downloaded. : If prompted, enter your Apple ID and password : Go to Settings > Privacy & Security