custom ringtone does not play for incoming call
A custom ringtone purchased from the App store does not play for incoming calls. The default tone plays instead.
iPhone 6 with latest iOS (11.1.1)
This is a known issue. You can certainly let Apple know you too are experiencing this via this link: Feedback - iPhone - Apple
You can also purchase and download a new tone and it will work, or you can create a new custom tone in Garageband and it too will work.