If you are a new DigitalOcean customer, you should start by signing up using our referral link. This will automatically add $10 in Cloud Hosting credits to your account.
Once you've signed up, you can also use a coupon code to add more credits to your account. To do so, start by logging in your DigitalOcean control panel. Once you've logged in, click the drop-down menu from the top right corner of the page and click on "Settings".
Select "Billing" from the left menu and scroll down the page where you'll see a box to enter your promo code:
If you entered a valid coupon code, you will then be able to apply the corresponding credits to your account. Note that you can use only one of the coupons intended for new users after which you won't be able to use those anymore.