You will need to set up at least one Formstack API Key. You can do this by logging into Formstack.com and clicking on "My Account" and then "API".
Next, click on "Create an API key" and fill in your API Key Description.
The permissions for your API key are tied to the permissions of the user who creates the key. If a user only has access to specific forms, their API key will only have access to those forms. Admin users will have access to all forms.