For the base URL , you don’t use the function names. Function names are added to the base URL
in order to reach the function endpoints. See the code in serviceModule.jsw to see how it’s done.
For a base URL for a free site in Preview:
https://{user_name}.wixsite.com/{site_name}/_functions-dev/
For a published site:
https://{user_name}.wixsite.com/{site_name}/_functions/