This deal popped up on Slickdeals early this month, but like many others, my Amazon account wasn't eligible when I tried it. The deal has floated up again because some people are now having better luck. So I tried it again and it worked for me this time.
It's a little odd in that it prompts you to log in even if you're already logged in, but it's an amazon.com URL, so I did it. I got the confirmation email shortly after and when I went to an ebook page, there was a little note right under the 1 Click button saying I had a $5 ebook credit. I ordered an ebook and it took $5 off.
I'm on my phone and having problems grabbing the Amazon link, so I'll just direct you to the Slickdeals page.
$5 Kindle eBook Credit
https://slickdeals.net/f/10979079-5-...gible-accounts
The credit expires 12/31/2017.