From Antonin in 370:

The PR improves info.magnolia.ecommerce.salesforce.common.SalesforceConnectionValidator. The validator evaluates connection configuration as valid for case when siteId is not equal to no-site and if a site with the configured siteId is returned for both: baseUrl and shopUrl.

Note: Configuration with siteId set to no-site creates a connection to all unassigned Salesforce catalogs, cart and checkout functionality will not work in this case, shopUrl isn't required.