Each Drip subscription has a single API Token. This credential is what gives other services access to your account through our API. Even if you have multiple accounts created under your subscription, your API Token is the same for all of your accounts.
Find Your API token under Settings > User Settings.
Scroll through the user Settings and you'll find your API Token towards the bottom of the page. Be sure to keep this a secret.
At times, Integrating your Drip account with another service will require entering your API Token into the admin settings of of that service. The credential will give certain types of permissions to the integrated service, and allow them to perform different actions in your account. This can be anything from creating and updating your subscribers, to firing events which can be used in automation and other places in your account. Generally these types of actions will vary depending on the type of service you're connecting to Drip.
You should take note, that, another service may not always refer to this credential as an "API Token." This type of credential is commonly referred to as an "API key" throughout the software service industry, amongst others.