HTC a9 SMS tone cannot be changed. After clicking Apply, it is still the default ringtone scheme.

Hello, I suggest you open the "Information" program-menu (three buttons)-Settings-Notification on your mobile phone, and then you can set the notification tone in the accepted notification.

If you still can't modify the SMS ringtone in this way, I suggest you back up the data of your mobile phone and restore the factory settings to see if it can help you restore your mobile phone to normal.

If the factory settings are still invalid, it is recommended that you back up your data and send your mobile phone to HTC maintenance center for testing.