They asked to somehow install Viber on iPhone 4 with the old iOS 7, which did not want to be installed through the App Store saying that iOS 8 and above was needed.
Installation performed as follows:
1) We connect the phone to the computer and try to install the application via iTunes, synchronize. When installing, a message should appear that the application requires a newer iOS (it should be so).
2) Now on the phone through the App Store we install the application (in this case, after we have completed step 1, the application will not require a newer iOS, but will install with an older version).
That’s all, and you can do without a dangerous jailbreak ;)