[EiresJason]

It seems like you just need to use an integer instead of the u specifier (which stands for username).

pawn Код:

new fid;
    new string[128];
    if(sscanf(params, "d", fid)) return SendClientMessage(playerid, -1, "USAGE: /createfaction [Faction-Slot]");

Also remove the strval function calls elsewhere like so:

pawn Код:

if(fid <= 0 || fid >= 16) return SendClientMessage(playerid, -1, "Invalid Faction ID. ( 1-15 )");