Apps on iOS generally only come from the App Store. These apps have been vetted by Apple and are safe. They are also signed by the developers who made them, and they meet all security requirements that Apple has set. That said, apps can come from outside the App Store. Getting them isn’t easy but it isn’t impossible. Sometimes when you try to run these apps, you get an error that it’s from an ‘Untrusted Developer’. All you can do is dismiss this error. It doesn’t tell you how you can run the app if you trust it. Here’s how you can fix the ‘Untrusted Developer’ error on iOS.
This applies to iOS 8 and later.
Fix ‘Untrusted Developer’ error
Open the Settings app and go to General>Device Management.
The app that you tried to run will be listed here. Tap it, and tap the trust option. Confirm that you trust the app and then return to your home screen. Tap the app and this time it will open.
A word of caution
While it isn’t easy to side-load apps on iOS, it has become relatively easier in the past few years. Users with a Mac can do it and often developers who have made an app that is highly unlikely to be approved in the App Store choose to distribute them as such. The code is put on Github with instructions on how to compile it. Given it’s open-source, you can probably tell if the app is doing something it shouldn’t but you’d have to be able to understand code which not everyone can.
What all this means is that there is a chance you end up with a malicious app on your device. If you are installing apps from outside the App Store, practice extreme caution on where you get them from. Apple tends to take security very seriously and if it chooses to exclude an app from its store, it likely has a good reason.
This error can also appear for apps that you’re beta testing or even ones you’ve developed and compiled yourself. You can run these apps the same way but if you’re looking to make the error go away for an app that you’ve developed, make sure you have signed it and that its security certificates are all correct, and up to date. In some cases, you might have to install a profile on your device to run some of these apps. Regardless, be careful with what you install and run.