iphone alarm is ringing once and not repeating

• Restart the device. That's it.
• Still not solved --> Force restart iPhone - Apple Support

Please check you may have enabled --> Settings > Accessibility > Touch > Call Audio Routing > Bluetooth [Ticked]

Please set it to Automatic.

Please see the pic below made on iPhone 12 Pro iOS 16.5. The two scenarios which I tested are given below and are self-explanatory

1. Check your DND status - If you're experiencing issues with notifications or incoming calls, it's important to check your Do Not Disturb (DND) status. On most devices, you can access this setting by going to "Settings" and selecting "Do Not Disturb." Make sure DND is turned off or adjust the settings to allow desired notifications and calls to come through.
2. Check BedTime status - If you're using the Bedtime feature on your iPhone, you can track your sleep patterns and set a schedule for waking up and going to bed. To check your Bedtime status, open the "Clock" app and tap on the "Bedtime" tab. Ensure that your sleep schedule is accurately configured, allowing your device to provide sleep analysis and reminders accordingly.
3. Check your Sound Volume - If you're experiencing low or no sound on your iPhone, it's essential to check your sound volume settings. You can adjust the volume by using the physical volume buttons on the side of your device or by going to "Settings" and selecting "Sounds & Haptics." Ensure that the volume is turned up and not muted.
4. Check your Ringer switch - If you're not receiving any sound notifications for calls or messages, it's important to check the position of your device's ringer switch. Depending on the model of your iPhone, the ringer switch is located on the side or top of the device. Make sure the switch is not set to the silent or muted position.
5. Check Call Audio Routing - If you're having issues with audio during calls, such as not hearing the caller or distorted sound, you should check the Call Audio Routing settings. On an iPhone, you can access this by going to "Settings," selecting "Accessibility," and then "Audio/Visual." Ensure that the audio routing is set to the desired option, such as Bluetooth, speaker, or automatic.
6. Check Auto Answer Calls - If your iPhone is automatically answering calls without your input, it's important to disable the Auto Answer Calls feature. Go to "Settings," select "Accessibility," and then "Touch." From there, disable the "Auto Answer Calls" option to regain control over incoming calls.
7. Check Connection with Bluetooth Audio - If you're having trouble streaming audio from your iPhone to Bluetooth devices, it's crucial to check the Bluetooth connection. Make sure Bluetooth is turned on in the device settings, and try reconnecting your iPhone to the Bluetooth audio device. If the problem persists, you may need to unpair and repair the devices or troubleshoot further using Apple Support resources.
8. Check whether in Headset Mode - If your iPhone seems stuck in headphone mode despite no headphones being connected, it could be a software issue. You can try solving this by cleaning the headphone jack with compressed air or gently inserting and removing headphones a few times. If the problem persists, you may need to seek assistance from Apple Support for further troubleshooting steps or possible repairs.