Second monitor is not detected through Surface Dock 2

I am attempting to run 2 monitors through the Surface Dock 2 hooked up to a Surface Pro X. Through the dock, I can easily run 1 monitor but it will not detect the second monitor. I can run the second monitor by directly connecting it to the Pro X while running everything else through the dock, but cannot run it through the dock. I have already ran an update. In display settings it will not allow me to "Extend Desktop" because it is not recognizing the monitor. Can you help?