The "device is not within the subnets assigned to beacon" message indicates that you do not have the beacon that is performing the inventory gathering operation mapped to perform operations on the subnet (IP address range) of the target device mapped. You can configure these details on the "Subnets" tab when editing beacon details in the UI, or on the "All Subnets" page.

With that said, if you haven't already considered it, you may want to consider gathering Oracle inventory using the agent. Using the agent is generally easier to manage and therefore a more reliable method for getting this data than attempting to manage the credentials, network connectivity and other aspects required to have a beacon make a remote connection to a server to gather Oracle inventory.