The error message, "Failed to set Adapter (com.esri.ges.adapter.inbound/JSON/10.2.2) properties: com.esri.ges.core.validation.ValidationException: Mandatory property 'ExistingGeoEventDefinitionName' is not set.", occurs when adding the 'Receive Features on a REST endpoint' input connector to a GeoEvent Processor, or when starting or stopping the GeoEvent Processor extension using the input connector.
The error is due to an unnecessary validation and does not indicate an actual error in the GeoEvent Processor or the adaptor. The error also occurs only when stopping and starting the GeoEvent Processor.