Hello,
In BC v28 and later, what you are doing is supported: Integration Field Mappings → New Field Mapping should open the Create New Integration Mappings wizard and allow you to add a Dataverse field without rebuilding the integration extension. The message “Generation has not been started. Start generation first.” is therefore not a normal field-validation error; it indicates that the wizard failed in its runtime integration-table/table-extension generation step before it reached Finish. First check that the new Dataverse field is enabled, is not a FlowField/FlowFilter, and uses one of the supported types such as Text, Code, Decimal, Date, Boolean, GUID, Integer, etc. More importantly, check your exact BC build: Microsoft released a 28.5 platform hotfix (ID 641662) specifically for the CDS “New Integration Mappings” wizard failing while generating a runtime table extension. The documented error for that hotfix is not exactly the same message as yours, so I wouldn't say with certainty that it is the identical defect, but it is the same generation path and I would definitely update/retest on 28.5 before troubleshooting the mapping itself. If it still happens on 28.5, expand Share details, capture the full AL call stack, and raise it with Microsoft because the wizard should not require you to manually start a separate generation process. As a temporary alternative, since this is a custom integration, you can still expose the field through an AL integration-table/tableextension and add the field mapping programmatically, which was the standard approach before v28.
Regards,
Oussama Sabbouh
