How do I set up separate verification codes in Passwords for two sites with a shared domain?

I'm trying to set up Verification Codes in Apple's Passwords for two sites that share a domain (top-level and second-level) but with different subdomains. But Passwords seems not to allow this. For example, I've got: - example.com - feature.example.com and when I try to set up either a password or a Verification Code for one, Passwords insists on saving it for the other as well. This is tolerable for password, since nothing prevents using the same password for different sites, but breaks for Verification Codes, because each of the above sites generates its own. How do I set up separate verification codes in Passwords for two sites with a shared domain?