What’s the matter with all message notifications on iPhone 6 showing beep sound but no ringtone?

Troubleshooting methods:

1. Is the text message prompt tone adjusted to "none"?

2. Is the volume of ringtones and reminders set?

3. Has the mute button on the left been adjusted?

If none of these problems exist, check to see if the Do Not Disturb mode in the settings is turned on, which is the small moon on the upper right of the screen. In front of it, there is a notification sound when the screen is on, but not when it is sleeping. I have studied it. The little moon is open below.