As the error message states: the combination of streaming session and reference id is already being used. This is most likely because you tried to create a new subscription using the same reference id. The ReferenceId must be unique each time you make a subscription. So when (re)creating a subscription, you must delete the previous subscription, or better, use ReplaceReferenceId to replace the old one with a new one. This saves traffic and narrows the gap between removing the old subscription and creating the new one. Below you can find an example of doing so.