Could you please confirm that you are referring to RM 2D barcodes which get printed for some of RM Shipping Services? If so, then the 2D barcodes will only be populated within the Tracking Number field for RM orders if you use the RM integration in LW.net.
However, you can still print labels from Linnworks desktop application and 2D barcode will appear in Tracking Number field in order details if use the LW.net RM integration in the Desktop. All you need to do it the following:
1. Integrate Royal mail in Linnworks.net: http://www.linnworks.com/support/shipping-management/courier-integrations/royal-mail/royal-mail-oba-shipping-integration/add-new
2. Add service that you want to use: http://www.linnworks.com/support/shipping-management/courier-integrations/royal-mail/royal-mail-oba-shipping-integration/edit-services
If same service name is assigned to desktop integration, then please make sure that you name it differently.
3. Assign new services to your orders and print order from Linnworks desktop application.
4. All you need to do from linnworks.net is file manifest in the end of the day.
Please note that 2D barcode will only be generated for untracked services. For tracked service Linnworks will still generate a tracking number.
Once the barcodes are generated, LW will send the tracking which will be saved under the Order details in Tracking Number Field along with the despatch note even if you use the Desktop client.
I hope this was helpful.