Hi there lucastheone,
If one of your AirPods isn't working, try the steps below to see if they resolve the issue for you:
If there's no sound in one AirPod
1. Make sure that your charging case is fully charged.
2. Place both AirPods in your charging case and let them charge for 30 seconds.
3. Open the charging case near your iPhone or iPad.
4. Check the charge status on your iPhone or iPad to make sure that each AirPod is charging
.
5. Put both AirPods in your ears.
6. Play audio to test both AirPods.
7. If an AirPod still isn't working, reset your AirPods or contact Apple Support.
You'll find those steps here, in the article that you viewed prior to posting: If your left or right AirPod isn't working - Apple Support
If the issue persists, the next best step is to have your AirPods inspected and serviced. This link will help you get started: AirPods Repair & Service - Apple Support
Take care.