I purchased ring tones on iTunes and it won’t let me download them

See -> Use tones and ringtones with your iPhone, iPad, or iPod touch

Use tones and ringtones with your iPhone or iPad - Apple Support

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Buy ringtones from the iTunes Store

1. Open the iTunes Store app.
2. Tap  More.
3. Tap Tones. 
4. Find a ringtone that you want to buy, then tap the price.
5. Choose an option to automatically set the ringtone. Or tap Done to decide later.
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8. You might need to enter your Apple ID password to complete your purchase.