This is a targeted offer. You can check it from your online AmEx account or app "AmEx Offers" section. When you spend $10+ using your registered AmEx credit card at McDonald's Canada locations before Dec 15, 2019, you will earn a $5 credit. Limit of 2 credits per registered card. I have 2 cards (AmEx Cobalt and AmEx SimplyCash Preferred) registered for this offer, so I can use this offer for totally 4 times ($20 cash back).
