Unable to add my card to Apple Wallet with iPhone 11

i only have 1 apple account and 1 card

Yes, that is good.

Try this -> Sign in to your Apple ID account page and edit / update your Apple ID details.

https://appleid.apple.com

On the Sidebar click Payment methods -> then tap Payments Methods and tap Manage payment method.

Or -> Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

See also -> Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

Click OK on your screenshot.

See the following Apple articles:

Set up Apple Pay

Set up Apple Pay - Apple Support

Countries and regions that support Apple Pay

Countries and regions that support Apple Pay - Apple Support (EG)

Set up Apple Pay in Wallet on iPhone

Set up Apple Pay in Wallet on iPhone – Apple Support (UK)

Try to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

Do you use multiple accounts?