[CalvinC]

pawn Код:

CMD:healall(playerid,params[])
{
    new string[200];
    LoginCheck(playerid);
    if(User[playerid][accountAdmin] >= 4)
    {
        foreach(Player, i)
        {
        PlayerPlaySound(i,1057,0.0,0.0,0.0);
        SetPlayerHealth(i,100.0);
        }
    }
    format(string, 128, "[HEAL] "white"Everyone has been healed by %s.", GetName(playerid));
    SendAMessage(COLOR_RED, string);
    } //-> Warning 3348
    else //-> Error 3349
    {
        SendClientMessage(playerid, COLOR_GREY, "You are not authorized to use that command!"); // if not, send him only the following message
     }
    }
    return 1; // This needs to be at the last bracket, so it symbolizes the command
}

Read the warnings/errors, first the warning, the command should return a value.
Which means you should have a return 1 inside the commands brackets, like above.

And about the "else", you do not have an "if" to activate it?
You might have meant to do underneath.

pawn Код:

CMD:healall(playerid,params[])
{
    new string[200];
    LoginCheck(playerid);
    if(User[playerid][accountAdmin] < 4) return SendClientMessage(playerid, COLOR_GREY, "You are not authorized to use that command!");
    foreach(Player, i)
    {
        PlayerPlaySound(i,1057,0.0,0.0,0.0);
        SetPlayerHealth(i,100.0);
    }
    format(string, 128, "[HEAL] "white"Everyone has been healed by %s.", GetName(playerid));
    SendAMessage(COLOR_RED, string);
    return 1; // This needs to be at the last bracket, so it symbolizes the command
}

Because you closed the "if" with a bracket, therefore the "else" cannot refer back to it. Using "return (function)" is a much better method though, so i changed it to that.