So if you have an existing DigitalOcean account, it makes it seem like you can't apply the promo code to it. But I shot off a ticket to DigitalOcean's support, and they applied the $100 promo to my account within 5 minutes. So definitely send them a message if you have an existing account that you would like to have the credit applied to. Awesome pack, and great service from DigitalOcean as well. Also of interest is…
Hm, that's nice of them, although this page states you aren't allowed to do that: "Keep in mind that we only allow one promo code per account, so if you’ve redeemed one in the past you may not add another. To see your promo code history please visit your billing page." https://www.digitalocean.com/help/pricing-and-billing/
"Contact DigitalOcean support with your unique promo code if you have previously redeemed a promotional offer, credit card required for activation"