Ringtone purchases
I purchased a ringtone song but I am not able to set it
Question marked as
If you have puchased a ringtone, follow all the steps and instructions in -> Use tones and ringtones with your iPhone, iPad, or iPod touch -> Use tones and ringtones with your iPhone or iPad - Apple Support
If you have puchased a song & want to use as a ringtone, you must first make that song suitable for a ringtone.
See this Apple article: Create and manage ringtones
Create and manage ringtones - Apple Community