I don't profess to know anything about APIs and stuff. So I dug out an old program called easy vsl. It wants to use watson via an api. Problem is I (think) I set it up all correctly, but it's still saying invalid API. I know I'm not giving you much to help me with. BUT, just taking a shot in the dark.
You might have more luck asking in one of the Watson community groups, I'm afraid this one is for IBM API Connect the product rather than general help about any API.
Good luck!