Forwarding is no solution here. That translates the destination address to another one, however, your crap device won't work with that, since the source address is out of another subnet.
What you need here is translating the source address into one out of the subnet of the concerned device and which is assigned to the pfSense interface, so that responses are sent back to pfSense.
That can be achieved by outbound NAT in pfSense. Firewall > NAT > Outbound
If the outbound NAT is still working in automatic mode, select the hybrid mode and save that setting first.
Then add a new rule. According to your example, select the VLAN30 interface (the interface facing to the problematic device), at destination enter 10.10.30.200, at translation address select "interface address" which is the default value. Save it.
Accessing the device should work now.