To log in to a Mac with a smart credential, the smart credential must be associated with the Mac user. There are a number of ways to do this.
Pair the mobile device and Mac as described in the app help.
Use the sc_auth command: sc_auth pair -u <user> -h <hash>. For more information, see the sc_auth man page.
By adding a configuration file that maps the Mac user to a directory, such as Active Directory, to each Mac desktop. For more information, see man SmartCardServices or the MacOS Deployment Guide: https://help.apple.com/deployment/macos/#/apdfe0b09fac