How does online CO2 exchange work via Amazon, Walmart, and Target .com?

Amazon 

1. When you order a CO2 refill at Amazon.com, cylinders come in sets of 2 with a label to return 2 empties ones for a $15 Amazon gift card.
2. Once you are ready to return the empty cylinders just register your email to start the return process: amazon.sodastream.com.
3. Place your empty cylinders in the original box with the USPS label that came with the set and send those back to us.
4. Please note it could take 1-2 weeks to receive the $15 gift card to your registered email address. Gift card offer is only valid on cylinders from SodaStream USA seller and Amazon.

Walmart & Target

1. Send us your empty two 60L SodaStream cylinders to get a $15 (Target, Walmart) Gift Card!
2. Visit gasexchange.sodastream.com for details and to start your exchange. Due to high volume, gift cards are issued ~2 weeks after receiving the empty cylinder.
3. Be sure to save the original shipping box in which these carbonators are delivered. The same box includes a USPS return label and must be used to return the empty cylinders for the Exchange Program.