Can't get GPU passthrough to work for VM

[bucky_BMX]

I'm trying to setup an Ubuntu server VM to run Plex and I'm trying to get GPU passthrough to work for hardware acceleration. When I try to finish the VM setup it gives me an error "Error while creating the PCI device. [EINVAL] attribute.pptdev: Not a valid choice". I have Virtualization enabled for the CPU in the BIOS of the host machine. There was also an option for "Single Root IO Virtualization Support" that I left disabled because I wasn't sure if it was needed. Any help would be greatly appreciated. Full error message and hardware specs below.

Error Message:
Error creating VM.
Error while creating the PCI device. [EINVAL] attribute.pptdev: Not a valid choice. The PCI device is not available for passthru: Following errors were found with the device: Unable to determine iommu group [EINVAL] attribute.pptdev: IOMMU support is required.
More info...
Error: Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 181, in call_method
result = await self.middleware._call(message['method'], serviceobj, methodobj, params, app=self)
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 1255, in _call
return await methodobj(*prepared_call.args)
File "/usr/lib/python3/dist-packages/middlewared/service.py", line 922, in create
rv = await self.middleware._call(
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 1255, in _call
return await methodobj(*prepared_call.args)
File "/usr/lib/python3/dist-packages/middlewared/schema.py", line 1152, in nf
res = await f(*args, **kwargs)
File "/usr/lib/python3/dist-packages/middlewared/schema.py", line 1284, in nf
return await func(*args, **kwargs)
File "/usr/lib/python3/dist-packages/middlewared/plugins/vm/vm_devices.py", line 168, in do_create
data = await self.validate_device(data, update=False)
File "/usr/lib/python3/dist-packages/middlewared/plugins/vm/vm_devices.py", line 308, in validate_device
await self.middleware.run_in_thread(device_obj.validate, device, old, vm_instance, update)
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 1172, in run_in_thread
return await self.run_in_executor(self.thread_pool_executor, method, *args, **kwargs)
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 1169, in run_in_executor
return await loop.run_in_executor(pool, functools.partial(method, *args, **kwargs))
File "/usr/lib/python3.9/concurrent/futures/thread.py", line 52, in run
result = self.fn(*self.args, **self.kwargs)
File "/usr/lib/python3/dist-packages/middlewared/plugins/vm/devices/device.py", line 45, in validate
verrors.check()
File "/usr/lib/python3/dist-packages/middlewared/service_exception.py", line 70, in check
raise self
middlewared.service_exception.ValidationErrors: [EINVAL] attribute.pptdev: Not a valid choice. The PCI device is not available for passthru: Following errors were found with the device:
Unable to determine iommu group

[EINVAL] attribute.pptdev: IOMMU support is required.


Hardware specs:
CPU - Ryzen 5 5600X
RAM - Corsair Vengence LPX 16GB @3600 Mhz
Motherboard - Asrock X570 Phantom Gaming 4
GPU for host - Geforce GTX 750 Ti
GPU for VM passthrough - GTX 1660 Super
Storage Drives - 2x WD Red Plus 4TB running in mirror configuration for data pool
Boot Drive - Inland Professional 256GB SSD
Power Supply - Thermaltake 600W
Chassis - Cooler Master HAF-X