Found the terms on another site. Here they are.
Valid 12:00 p.m. (PT), July 16, 2018 through 11:59 p.m., July 17, 2018 (PT).
Promo code will be valid through September 2, 2018 11:59:59 PM (PT).
Taxes, shipping and handling, and gift wrap charges, if applicable, do not apply when determining the minimum purchase amount.For qualifying purchases, a promotional credit of $5 will be automatically applied to the Amazon.com Prime account that was used to purchase the Amazon.com Gift Card(s) within two (2) days after the qualifying order has been completed or, where applicable, the order has shipped.
Limit one promotional credit per Amazon.com Prime account as designated by the primary email address.
The promotional credit only applies to products and digital content sold by Amazon.com or Amazon Digital Services LLC (look for “sold by Amazon.com” or “sold by Amazon Digital Services LLC” on the product or content detail page) and all eBooks made available through Amazon.com. Products and digital content (except for eBooks) sold by third-party sellers or other Amazon entities, including Prime Now LLC, will not qualify for this offer, even if “fulfilled by Amazon.com” or “Prime Eligible”.
The savings from the promotional credit will be reflected on the final checkout page of qualifying orders.