AirTag koppelt niet

Hello Peterseuntjens, welcome to the Apple Support Community!

This is a problem that often happens if the AirTag needs a little system cleaning. To fix this, turn on Bluetooth and Wi-Fi on your iPhone. Then, reset the AirTag: How to reset your AirTag - Apple Support (open it, remove the battery and put it back by pressing it until you hear a beep, and repeat this step 5 times in a row). At the fifth noise, close it and bring it closer to your iPhone XR to restart the association. If necessary, you can consult the article How to add an AirTag to Find My - Apple Support. Have a nice day :)