[ReneG]

pawn Код:

if(sscanf(params, "is[24]", targetid))

The sscanf specifiers you are using do not match the command you are making.
If you want the command layout like.

Код:

/makeleader [playerid/PartOfName]

Then use the u specifier.

pawn Код:

COMMAND:makeleader(playerid, params[])
{
    if(PlayerInfo[playerid][Adminlevel] < 1) return SendClientMessage(playerid,COLOR_ERROR,"[ERROR]: You are not authorized to use this command ");
    new targetid;
    if(sscanf(params, "u", targetid)) return SendClientMessage(playerid, COLOR_SYNTAX, "[SYNTAX]: /makeleader [PlayerID/PartOfName]");
    if(targetid == INVALID_PLAYER_ID) return SendClientMessage(playerid,WHITE,"[ERROR] Player Is Not Connected");
    else
    {
        SendClientMessage(targetid,COLOR_GREEN, "You have been made a faction leader!");
        FactionLeader[targetid] += 1;
    }
    return 1;
}

You also included two variables for no reason when you only needed one.