I need to pay monthly for airtag

Hello blas48.

Thank you for using Apple Support Communities. It sounds like you're asking if you need to pay monthly to use AirTags. If so, we'd like to share some information with you.

There is no subscription service fees for using AirTags. We do have a couple of resources below that you can review on how to set up AirTags with your device:

Set up your AirTag using your iPhone, iPad, or iPod touch - Apple Support

Add an AirTag in Find My on iPhone - Apple Support

We hope this information is useful. Cheers.