Hopefully, with these instructions, you'll find your API Key before you find Waldo.
Login to letterdrop.com
Select the publication you want to manage via API
Click on the Settings icon either on the main page or from the menu dropdown in the top right
Scroll down to API and Webhooks
Copy the API key provided
You can click on the regenerate button to create a new API key at any time. Keep in mind that this will expire the old key.
You have to include your API Key in the
api-key field of the header of your API requests.
Check the field
api-key for your API Key in the header of webhook requests to your endpoints.