How do I tell the game that everyone is ready Multiplayer?

I have a multiplayer interface and I wanted the game to return true when all players were ready

First I tried to follow this tutorial but it didn’t work

I know this is old but maybe could help someone, this is what I am using for a seamless travel join from a lobby

Add clients to a current players array. This is called for each client joining.

void AMyGameMode::GenericPlayerInitialization(AController* Controller)
{    
    Super::GenericPlayerInitialization(Controller);

    CurrentPlayers.AddUnique(Cast<ACP_PlayerController>(Controller));
}

Then check the current players against the traveling players

bool AGM_Gladiator::IsAllLobbyPlayersConnected()
{
    TArray<AActor*> ActorList;
    GetSeamlessTravelActorList(false, ActorList);    

    if(CurrentPlayers.Num() == ActorList.Num())
    {
        return true;
    }

    return false;
}