An API Key is required to use the REST API. Read more about the REST API
Your keys can be found by visiting API Keys.
You can create new API Keys by clicking the New API Key button and entering a name, for your reference.
Using the to.co REST API will cost you Data Credits. From the API Keys page, you can check how many credits you have left and have used.
If an API Key has been used, you can check how many requests have been made and how many credits have been used since it was created. View the recent activity by clicking the Activity button.