Problem
When using the /workspaces/:workspace_id/vars API endpoint, the following error is shown.
{"errors":[{"status":"404","title":"not found"}]}
Cause
The /workspaces/:workspace_id/vars API endpoint was added in Terraform Enterprise v202001-1. If using an earlier version of Terraform Enterprise, you must use the /vars API endpoint instead.
Solution
In order to use the /workspaces/:workspace_id/vars API endpoint, please upgrade to Terraform Enterprise v202001-1 or later.
Additional Information
Here are the links to the documentation for both API endpoints.