Aws_lb_listener_rule - Weighted Target groups - Error

I am trying to add 2 target groups to a single listener in AWS usign terraform 0.11.
Though the official terraform registry documentation( includes ‘Weighted target groups using forward block’, when I try to use that, am ending up with an error ‘aws_lb_listener_rule invalid or unknown key: forward’.
Could anyone please help me on this.

hi there, any luck on this?