That's weird. When I run the same test script I was using yesterday, I'm now getting meaningful error codes and responses.
Code:
curl \
-w "%{http_code}" -o "result.txt" \
-H "X-API-Token: MYAPITOKENHERE" \
-F "id=23261" \
-F "version=7.0.3.2" \
-F "compatible=7.0.3" \
-F "[email protected]" \
"https://api.wowinterface.com/addons/update"
Yesterday this (with a missing or invalid API token, or a missing "id" field) was printing "00000" in the terminal, and not creating a "result.txt" file. Today it's printing 403 in the terminal (with a missing or invalid API token) and a useful message in result.txt. (Missing addon ID is 404, invalid addon ID is 401 even for addon IDs that don't exist yet on the site.)
Though, there is a typo in the error message:
Code:
{"ERROR":"You must be authenicated to use this API."}
I'll keep an eye on it and let you know if I see anything weird again.