I notice below:
So the "database" service is not recognized. The IP addresses of the devices are identical with the DB Service so I thought this would work.
Because this is a plugable database the DB Service process is not a database process but a listener, and part of a SCAN service.
Could the above be the reason for not picking up the service in the custom device?
In short - yes, it might be the cause.
But it would be a lot easier to guide you if we’d have more details. Pluggable DBs should be related to the DB service (client side) if all the criteria are met, but to diagnose that please provide more details in support ticket.