I stumbled across this deal today and RAN out to take advantage of it! Head over to Amazon and log in to get your bar code, take it to a participating store (I went to Cumberland Farms) and add $20 to your account and they will give you $10 for FREE!!! I had my bonus credit in my account within minutes.
Note, this is a limited time offer, one per Amazon customer account. Promotional credit expires at 11:59 p.m. (PT) August, 31, 2017. Offer only applies to products sold by Amazon.com. For additional details about Amazon Cash, see the page here, the Amazon Cash FAQ and the Promotion Page for complete terms and conditions.