Initially I had the same issue.
(taking a look see at the lesson I'm assuming you mean)

after messing with it a bit...
I think the key is transferring pressure to the G string
(AFTER bending it up with the B string)

after messing with it for a few moments...
I found I could get brief sound from G string
but it instantly dies
then I could get it to last a bit longer; but not full descension in pitch.
and my conclusion is that's just a coordination issue.

this isn't a priority for me right now so that's where I'm leaving it.

but I think I'm on the right track with how it works;
I'm just having trouble executing.

so my conclusion is:
it's just like it says in the lesson description:
"The mechanics of this technique can be pretty challenging at first, but it's an incredibly useful tool and completely worth the hard work!"

(so you just gotta mess with it and alter your approach and observe if that's giving you a slightly better result; or not.