This wikiHow teaches you how to allow installation of apps from outside the Apple App Store on your iPhone.
Step
Method 1 of 2: Installing Untrusted Apps
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Step 1. Download and install the custom app
This application is made by the developer for the company's internal use. For example, you may need to install a customer management application, or an application to download data from the Web.
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Step 2. Open the app
You'll see an "Untrusted Enterprise Developer" warning.
Apps you download from the App Store will get trusted status automatically
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Step 3. Tap Cancel
Method 2 of 2: Trusting Special Apps
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Step 1. Tap the gray cog icon (⚙️) on the home screen of the phone to open the Settings app
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Step 2. Tap on General option
This option has a gray cog icon (⚙️) in one of the sections above the menu.
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Step 3. Tap Profiles
This menu may have labels Profiles & Device Management.
This menu won't appear on your iPhone until you install and try to open an untrusted app
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Step 4. Tap on the name of the app developer in the "Enterprise App" section
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Step 5. Tap Trust [Name of Developer] near the top of the screen
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Step 6. Tap Trust to allow iPhone to run your installed apps
In addition, applications from the same developer will also be automatically trusted.