Port knocking on the 2767ax

I'm trying to set my new router up for Teleworker VPN and my understanding of the arcane instructions is that when I Enforce Port Knocking in the General tab, set the 1st Knock Port and click Apply a validation window should pop up for me to enter the code from the Port Knocking Tool. This doesn't happen. I have tried disabling the popup blocker in Firefox and I've tried it in Edge but still no popup.

Can anyone tell me where I'm going wrong please?

Mike

OK I finally solved it. There is a Reset button on VPN > Teleworker VPN > General and clicking this caused the Validation pop-up to appear.

Port knocking is working 

Mike