Connecting to a Salesforce sandbox with the Salesforce connector does not work. How can I connect to Salesforce Sandbox?
Use the Salesforce sandbox connector instead, as seen in this image:
When Fivetran connects to Salesforce, we will try to connect via login.salesforce.com, but when using the standard Salesforce connector which is the URL for production Salesforce org. This will fail if you are trying to connect to a sandbox org because Salesforce sandboxes must be logged into via test.salesforce.com.