Hello Lonbear,
Thank you for using Apple Support Communities. Sounds like you're unable to set up custom ringtones. If so, we'd like to help out. First, you might want to try refreshing things by restarting your device. This can sometimes sort out unique issues: Restart your iPhone - Apple Support
If that doesn't help out, we'd like to further isolate this issue. Try using a different ringtone and see if it reverts back. This information will let us know if there's something wrong with the special text tone you're trying to use. If the special text tone was a downloaded purchased text tone, try deleting the purchase and then redownload it. Once you've redownloaded it, you can test again and see if you're able to apply that text tone.
To delete a download ring tone, follow these steps:
- Go to Settings > Sounds & Haptics.
- Under Sounds and Haptic Patterns, find the ringtone that you want to delete.
- Swipe left over the ringtone, then tap Delete.
Steps on how to redownload your ring tone, click here: Use tones and ringtones with your iPhone or iPad - Apple Support
Redownload ringtones purchased with your Apple ID
1. Go to Settings > Sounds & Haptics.
2. Under Sounds and Haptic Patterns, tap any sound.
3. Tap Download All Purchased Tones. You might not see this option if you already downloaded all the tones that you purchased or if you haven't purchased any tones.
*You might not be able to redownload some previously purchased tones.
We hope this helps out. Thank you for using Apple Support Communities. Take care.