Amazon is promoting its shopping app (download here) by giving out credits to target users. Click here on your mobile phone, open your Amazon app, if you’re targeted you’ll see below message: “Claim your $15 coupon for First App purchase now!” And you can claim another one in 24 hours, for a total of $30 credits.
Note, it says “for your first purchase,” however multiple users reported that it worked while they are not first time user. My account has this offer, too (I made the screenshot on my Andorid phone), despite that I made a lot of purchases already in the app. You can use the coupon in-app on items of $25 or more, ships from and sold by Amazon. Below screenshots show how the $15 credit was applied in my order of Nespresso Vertuo coffee pods.
The credit was labelled as “App first sign-in” but I’d actually used Amazon app many times before.