This might help if your Fire came with 5.1.3 or 5.1.4:
I mustâve missed something, because I got an email from Amazon saying I didnât get the $10 discountâŚso they sent me a gift card instead.
Thank you for shopping with Alexa during our Prime Day celebration.
Because you purchased a product using Alexa which was not eligible for
our $10 discount, we wanted to give you a $10 Amazon.com Gift Card to
thank you for trying Alexa voice shopping.
Sometimes retailers are not allowed to discount products. Instead of Amazon listed every single one, this was likely their unpublished policy to deal with the issue. Amazon tends to do this kind of thing.