Invite friends
What I need to do for invite my friends to have the Apple Card
Are you wanting to invite them to be Participants (Authorized User) or just send a link to apply for their own account?
Set up Apple Card Family and add a co-owner and participants - Apple Support
There is also a Sign Up Bonus (SUB) for new applicants. You get the link by the following path,
iPhone > Wallet app > Apple Card > More button (3 dots upper right corner) > Daily Cash > scroll down for offer (see image below).