Validate that the port from the ATA and/or VG is connected to the correct wiring pair/port on the device for the CO line, and that the dip switches on the unit are set appropriately per the guide. It can be configured for ground start, which the ATA/VG is not. It can be configured for a page port or override with contact closure, which the VG is not either.
The instructions for this mention 1A2 and other key systems so I imagine this is an older device, and it may not be happy if the voltage produced at the device is not Bell spec, but, I've yet to really have any issue with that and any page device I've tried.
I would validate at the device with a test set that it is ringing in, the output voltage is acceptable, and that this paging device is configured correctly for a loop start CO trunk. Other than that you would need to meter and see how it is looking and then reach out to Valcom, I have never used it directly so I can't say much more about how it works or what the problem would be.