Pedro are you getting your API key from within the Cloudability tool mate? (Manage Profile, Preferences)
What tool are you using to make the API call?
If you're using CURL make sure you have a colon on the end of your key between the single quotes.
https://help.apptio.com/en-us/cloudability/api/v3/getting_started_with_the_cloudability.htm
If another tool ensure Basic is selected as the auth type and that the key is in the user name field.
#Cloudability