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