This error can be caused due to a lack of access.  Check the following:
  • Confirm the API Username is correct.
  • Confirm the API Password is correct.
  • API user has the correct permissions for the call you are making.  
  • Confirm no group overrides are included on the API permission type used by the API user. (When you create an admin group overrides for certain security categories can be set- any permissions used by an API user should have no group overrides configured)
If you need more information on creating an API admin record: How do I create a username and password that can log API calls in Luminate Online?