Can someone tell me?

[AidanClover]

Can someone explain to me the whole FSL thing and why Requiem / Disturbed doesn't allow you to go into online multiplayer? Havent used this for 4+ years or played 

[MrDario]

FSL is a workaround to go into Public Sessions (while being Host) with BE disabled and Requiem injected, without FSL you would be unable to open a Public Session as you would be kicked for having BE off, on the other side you're free to play in Invite Only sessions even without FSL.

[Stimulate]

Note: Your progress won't be saved to R* servers when playing with FSL since everything will be stored locally. With Invite Only sessions it'll still be saved.