ArcGIS Server: Connection property set missing required property or property value unrecognized. Invalid connection property

Error Message

Validating the relational data store using JSON in the ArcGIS Server Administrator Directory fails and returns the following error message:

Error:
The connection property set was missing a required property or the property value was unrecognized. Invalid connection property.[]

Additionally, attempts to validate the relational data store via ArcGIS Server Manager fail without returning an error message.

Cause

Port 9876 (TCP) is closed, preventing proper communication with the relational data store.

Solution or Workaround

Enable port 9876 (TCP). Refer to ArcGIS Enterprise: Ports used by ArcGIS Data Store for additional information.

Note:
Contact the organization's IT personnel to enable port 9876 (TCP).