Your Salesforce Org, or your User, might have the API Disabled. If so, you will see this error message:

If you are a Salesforce Admin, you can fix this. If not, you may need to show this article to your Salesforce Admin.

Steps to Fix

  1. Go to the Salesforce Setup. In Lightning, that's the Gear icon in the upper right.
  2. In Quick Find, search for Profiles.
  3. Go to that particular Users profile and click on Edit.
  4. In Administrative Permissions, API Enabled should be checked.