Adding Coupon/Pass to Apple Wallet

I received an email from a car dealer with a link to a web page with coupons on it. Going to that web page on my iMac I see each coupon has an official-looking "Add to Apple Wallet" button. Clicking one of those brings up a QR code.

So on my iPhone (6s, 10.3.3) I go to the Wallet app and touch "Scan Code" and hold it up to the iMac screen. The code is found but it says something like "No pass for this code".

If I instead go to that web page in Safari on my phone, when I tap the "Add to Apple Wallet" button I get "Safari can't download this file". So no joy (I just printed the coupons from my Mac).

Was this a problem on their end setting up these coupons, or am I missing something on my phone? I use Apple Pay with a credit card without any problem, but haven't used passes before.