You’ll be able to take advantage of the Amazon Music Unlimited free 30-day trial, meaning you won’t have to pay anything to lock in today’s deal. Though it will auto-renew, so be sure to cancel to avoid any unwanted charges.
New Amazon Music Unlimited Subscribers | Dot for $1 (US Only) Expired
JDRoberts
#2
your most recent order must have been made with a US credit or debit card. Only available to customers located in the U.S.
Looks like following the directions immediately sets up the future recurring charge on the credit card you used for your most recent Amazon order. So just be aware of that. 
RightHand
#5
“Available quantities have been redeemed” is the message people are getting now.
Once it made it to Slickdeals…And then you have people that abuse these promotions.