Can’t update iPhone 6s Plus
Currently having 13.4.1 version of iOS but whenever I tried to update, it fails at the end without errors.
You should be able to update to iOS 15.7.7 assuming that you have sufficient room on the device.
Is updating using a cable and a computer a reasonable option for you?
Update your iPhone, iPad or iPod touch with the Finder – Apple Support (AU)
or
Update your iPhone, iPad, or iPod touch with iTunes - Apple Support
