On Tuesday, during Amazon’s Prime Day, festivities, the online retailer’s credit card partner Visa joined in the fun with a promotion where customers who made a $150 purchase using their Amazon-branded Visa card would receive a $30 discount. That’s an appealing bargain, and plenty of customers prepared to take advantage of it. What they didn’t do was read the fine print, or take it seriously, and a lot of customers missed out.

Let’s start with the email that went out. Not all Amazon Visa users received it; we’re not sure which customers were targeted.

The email does say “restrictions apply” pretty prominently; let’s see what those restrictions were.

This is a limited time offer while supplies last. Offer limited to one per eligible customer and account. This offer is available to select customers only. Get $30 off an Amazon.com purchase of $150 or more by selecting your Amazon.com Rewards Visa Card as your payment method and entering the promotion code VISA30 at checkout through the Amazon.com shopping cart. Offer only applies to products sold by Amazon.com.

That’s all very reasonable, but those first three sentences are the parts that aren’t spelled out in the main body of the email. Later, on Amazon’s site, they added a line to the conditions of the promo, specifying:

“Get $30 off an Amazon.com purchase of $150 or more by selecting your Amazon.com Rewards Visa Card as your payment method and entering the promotion code VISA30 at checkout. Promotion code commences at 12:00 a.m. (PT) July 12, 2016, and expires at 11:59 p.m. (PT) July 12, 2016.”

“Amazon created restriction after restriction that made it impossible to purchase anything of value,” an anonymous reader wrote to Consumerist. “It was like going to a garage sale on the last day …the only thing left is junk. They taught me well: never chase an Amazon promotion again.”

Customers received different explanations about what happened to the code and why it didn’t work, which is makes this situation so strange. Reader Chris turned to Amazon customer service to complain about the deal, and was told that Amazon ran out of discounts.

Chris: The terms and conditions in the email I received do not state any end time. They only scope the date of redemption to Prime Day, and today is Prime Day.

Amazon Chat Agent: I’m sorry for that Christopher, as informed this was a limited time offer, while supplies lasted.

Chris: I was not informed of a time limitation or a supply limitation.

Customers posted on Amazon that they were also told that the deal really expired at 12:30 PM Pacific time, or that the expiration time spelled out in Pacific time were actually in UTC.

This raises an interesting question: how can the “supply” of a discount run out? If Amazon and Chase decided that only the first 10,000 customers would receive the discount, for example, then it makes sense, and that fits in with the limited-quantity deals that fill the rest of Prime Day.

If you imagine that Amazon had a fixed number of virtual $30 discount vouchers, this statement makes sense. At a physical store, when the stack of coupons runs out, they’re gone.

At the same time, it would have made the promotion even more fun and would make customers clamor to shop even more if they had known that quantities were limited. The discounts ran out around noon Pacific time, and disappointed customers complained online, on deal forums, and complained to Consumerist.

It’s really great that the companies provided credits to these Amazon customers, because they were under no obligation to. While the ad simply said “during Prime Day,” it specified that the promotion was only good while supplies lasted. The time restriction came along later.

Sometimes you have to crank up the type size on your screen and read the fine print. There’s no way around it. At the same time, though, this promotion could have been explained to customers better, and shoppers wouldn’t have been so upset about it.

We contacted Amazon and Chase about the promotion. Chase declined to comment on the situation except to point out that the affected customers did receive gift cards. Amazon didn’t respond: if it does, we’ll update this post.

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