Primary or Base URLs is the default test URL for loading website to editor, generating previews, and reports. The Editor URL should be a valid URL without any pattern (wildcard) or regular expression.
For example, you have specified multiple pages to run a test using URL pattern. VWO will not understand which page of the website to load in the visual editor, or which page should be used for generating test previews, and other actions. This base URL will be used as the default test URL and used wherever required.
By default, VWO populates the primary URL field based on the test URLs you entered. You can edit the default primary URL according to your test requirements.