[Scenario]

Why are you using "strlen"? Just do:

pawn Код:

CMD:test(playerid, params[])
{
    if(isnull(params))
        return SendClientMessage(playerid, COLOR_WHITE, "USAGE: /test [param]");

    SendClientMessage(playerid, 0x123456FF, "This is a test message!");
    return 1;
}