Amazon has brought back a popular promotion for Music Unlimited where you’ll get 30 days for free, plus a $10 credit applied to your account after the free trial. The promotion is for first time Amazon Music Unlimited subscribers and it’s easy to know if your account qualifies. Those who qualify will see the text “$0.00 per month – The following promotion applies after your free trial: $10 promo credit” displayed on the page. If you don’t qualify, it’ll simply say “The promotion is not valid” in red near the top of the page.