Your API Token/ Key is a string of letters and numbers that is private to your account. Do not publicly disclose your API key. If you do, you can generate a new token, but just know that anything using the old API key will no longer work.
API Key Example: ba534d4274523452345da0e99345a67000
When entering your API key it will most likely be in the form of a Header {Value: Key}.
You would enter in your API key like this:
Authorization | Token ba534d4274523452345da0e99345a67000
Note: The format has to match in order for this to work.