just started the game and learned how to use the fulton device at mother base; ocelot tells me to fulton a group of guys after knocking them out but the device is unavailable (red line through symbol); ocelot keeps telling me to fulton the guys but i'm unable to do it

You have to do it with an unobstructed line to the sky, eg outside.

Also I think guards need to have been stunned or put to sleep through your actions.

I don't think it works on guards who are already sleeping (because they are resting between shifts) or a guard that you have held up and told to lay on the ground.

EDIT:

Ignore this, @ghostiet is totally right!

Maybe I was thinking about not being able to pick up guards who are just laying down after being held up.

Nope, absolutely works. They even scream for help if you forget to knock 'em out before fultoning them out.

i got the device from ocelot and the sky was clear, it was the heli landing pad where ocelot teaches you how to use it; i knocked out five guys and ocelot keeps saying "okay, go on and extract them" but i can't

i think i know; the base has too many personnel

@laudasolem said:

Even if your Mother Base teams have max capacity, you can still fulton people to your base. They'll just sit in the waiting room... at least, I think that's the case? I must have had 100+ people in the waiting room at some point so if there's a limit, I imagine it must be massive.

Maybe your out of fultons for some reason, call a supply drop. Or better yet just reload your save first and then see if you have the ammo if not call a supply drop.

i don't know what's happening at this point, it's not a glitch; i'm missing something somewhere

^Go to development and see if it's made, did you try and call a supply drop? And it sounds like it is definitely a glitch

Can you take some video of trying to fulton someone, along with some screenshots of your R&D screen where the Fulton device is? Even just the screenshots would help. It sounds like you may be missing a piece of research.

@ghostiet: If i "forget" to knock them out ;)

There is a limit and after you hit that limit the guys you fulton gets instantly discharged.

How could OP have hit this limit before doing the fulton tutorial?

+1 to @Mike asking for a video. Sounds like a glitch to me though; Ocelot shouldn't be saying to try extracting if you can't. When you hit "back" do you have the option to go back to checkpoint and/or "restart mission"? Since it sounds like some scripting just went wrong.

WRONG. It auto discharges the the weakest people across all your staff so if you're totally full of guys and you fulton a high ranked guy he will replace the weakest person on your staff.

Also I will add before you unlock the fob the cap on people is 700 and with the fob its 1400 and if you get a second fob the cap is 2100.

moved on to mission 2, where i had to eliminate/extract the spetznaz officer; the fulton thing was working fine so looks like i'm ready for more intense tactical espionage action

...OK.

I'm just going to close this thread since everything is working now.