UD22, Chromebook, dock DP not working with external display

Dear Support team, 

As we are using Chromebook,

External display is not lighting up connected DP port of external display to Dell Universal Dock UD22 DP port.

Connected USB-C end of the dock to our Chromebook and external display connected to UD22 DP port.

Whereas the same external display lights up with other Dell dock model (Thunderbolt Dock WD22TB4) which is connected to USB-C side.

1. Could you please help me if there is any firmware that needs to be specifically updated w.r.t Dell Universal Dock UD22?

2. Or is there anything or as per detailed specs, could you please share us the same of Dell Universal Dock UD22 Vs Dell Thunderbolt Dock – WD22TB4 (which is connected to USB-C side.)? 

3. May I know what is the key differences between Dell Universal Dock UD22 Vs Dell Thunderbolt Dock WD22TB4 (which is connected to USB-C side.)?

Many thanks in advance.