I want to add my card as payment method to my Apple ID

If you want to add it to your Apple ID and not Apple Pay, then follow the steps in the support document linked below.

click here ➜ Add a payment method to your Apple ID - Apple Support

You can follow this guide to add a credit or debit card to Apple Pay: Set up Apple Pay - Apple Support

Try this: Set up Apple Pay - Apple Support

Note: You have to be 16 yrs old to add a Payment Card