This is NOT a referral service or anything off the sort. I stumbled on this months ago myself and have been using it quite a bit. I don't see anyone on here having discussed it, so I thought my fellow SD'ers would appreciate this. Simply go to the website and sign up:
Basically, Vipon is a marketplace where Amazon sellers will post deals for free or heavily discounted items. A lot of them (most, I daresay) are useless. However, the great thing is that a good number of them are under a dollar, and fulfilled by Amazon. So you can basically pay 20 cents for some crap you don't need and get no-rush shipping. So you get the item plus a $1 digital credit for 20 cents. Your can 'request' 150 items a month. You won't get most of them, but you'll get a few, which is all that matters. The company will then send you a coupon code. About 80% of the time it works (they've been getting better at weeding out sellers who make posts with non-functional coupon codes).
I posted a picture of a recent order I made as an example. I paid 13 cents for some brita filters I can't use, but can give them away to a friend, and got a dollar digital credit for it.
Over the past couple of months I've probably spent $10-15 on products, a few of which come in handy and many of which make decent gifts. With that amount I've probably gotten $50 in MP3 credit. Pretty great service if you already have Prime. I like to use it as a moneymaker, but there are some good deals to be had (I bought a $2 USB type-c cable today and got the $1 digital credit too, solid deal).
Delete this if I'm violation of some rule. I hope not. I suspect a lot of a SDers will love this.