Can't get app to apply for Apple card

Are you wanting to apply from an iPad or an iPhone? If you're trying from an iPad, I don't believe you can put the wallet app on an iPad. You'd have to use the web based application

apply.applecard.apple

This is a user to user forum. No one here can answer why; we don’t even know who you are. There are dozens of possible reasons, but if you start with this guide you may be able to figure it out for yourself—>Steps to take for applying to Apple Card - Apple Community

Are you a US resident over 18?

Good catch. I assumed an iPhone because the post is in the iPhone forum.