Facebook instant games - create a multi-player game

[Bonomi]

I've been learning how Facebook instant games SDK works in multi-player mode for a while and still don't have a solid idea. 
Looking at the function "chooseAsync" it seems to be the one that a player (player A - master) uses to invite a friend (player B - slave) to play the game with you, fair enough. 
But then, how do we handle the accept request on player B (slave) flow?
How is player A notified that his friend accepted the challenge and is ready to play?

Same questions about when one player is waiting for his opponent to play, I believe I need to use "switchAsync" function but am a bit blurry here as well,

[Noel]

@Bonomi What kind of game are you making? Is it turn based? Do you have a server side?

[Bonomi]

@Noel the game is very similar to the tic tac toe, it is turn based and I have a backend.

[Noel]

@Bonomi
Got it. Have you read the documentation? https://developers.facebook.com/docs/games/instant-games/guides/play-friends

1- But then, how do we handle the accept request on player B (slave) flow?
Once player B enters that context (see the documentation I shared above) it means the challenge is accepted, it is that simple. Then you can handle it on your server side.
When player B has played his turn, you could send a custom update: https://developers.facebook.com/docs/games/instant-games/guides/game-update

2- How is player A notified that his friend accepted the challenge and is ready to play?
See answer 1.

3- Same questions about when one player is waiting for his opponent to play, I believe I need to use "switchAsync" function but am a bit blurry here as well.
Not sure what you mean, but I feel my answer to 1 answers this as well.

[Superatons]

I do not understand how to implement the following link   with socket.io

[Noel]

@Superatons And I don't understand your question. Could you provide more information?