Trouble with guest network

Good morning all.
Noobie here (again)
I have been running my linksys wrt1900ac v1 for a few months now and all is working great.
I have successfully added a adblock on and also works well.
I would like to set up a guest network on it that runs through a vpn (surfshark) wire guard is also installed.
I have followed a few youtube videos and also a few posts on here. But no luck. When i connect its not giving device a ip and fails to connect.
Does any one have a fool proof guide i can follow please?
Thankyou for taking the time to read this.