Token
If you use API, you need an API token.
You can get a token in the Smelter interface.
To do this for the first time, go to the Account → Settings page and click Contact us.
How it looks like
You will have access to API.
How it looks like
If you already have access, click Recreate API Key and in the pop-up window click Copy.
How it looks like
More about authorization with a token read in the Smelter API part of Help Center.