Update: Found the cause of the issue. D3200 does not allow shutter control via USB when in Bulb mode (not an issue with the D3500). I have tested outside of Bulb mode and the process works as expected, albeit tied to the exposure settings on the camera body.
I have found a couple of homebrew solutions which involve hacking together the USB cable with the remote cable. Not ideal.
If anyone has any experience of this and/or an alternate solution please update this topic.