It's possible to only return tracking numbers to eBay for Tracked services with Royal Mail rather than for all Royal Mail services.
To only send tracking numbers for Royal Mail Tracked services back to eBay, go to the eBay settings page and select Advanced Settings. At the Royal Mail Tracking Numbers option select Only send for shipments with Trackable service.
Select the Save button.
If you have any questions about this, our support team would be more than happy to help!