In my experience Google Fi is never coded correctly, at least for Amex charges. I supposedly should get $10 off per month if I use my Biz Plat to pay for my wireless bill. These had never been credited. I brought this up to the customer representatives and opened cases many times. They are never resolved in my favor. I've given up since.

But, good luck to you and others who are trying for this offer. I hope you guys have better luck than I do.