Amazon has been doing that for years. I was offered AWS credit when I took a machine learning course at Hacker Dojo a few years back.
The first one is always free.
According to the pricing section of the Verified Certificate page, the minimum fee varies by course but I can't find a way to determine the minimum fee without an account.
Which indicates the minimum fee is a $50 contribution.
It feels like edX could do much better in making that pricing information available before enrolling but perhaps their testing has indicated otherwise.
Definitely one of the better quality MOOCs in terms of content and production values.
I'm absolutely going to sign up again and follow through given the incentives.
Either way, it's cool seeing Amazon offer this to people who are interested.
If they want people to take their certificates seriously, I guess it would be important for people to trust that the person listed actually earned it. The documentation may also improve later conversion to paid products as well avoid the same person passing the course multiple times with multiple AWS accounts to get more AWS credit.
(FYI, AWS gives $100 credits quite readily for on-line course takers in general.)
Whatever Account # you provide to edX is the one that will be associated with the credit.
You can also get $100 in DigitalOcean credit here: