[MarvinPWN]

At the end of the callback OnPlayerCommandText you have to return this message.
Look here:

PHP код:

public OnPlayerCommandText(playerid, cmdtext[])
{
    if(!strcmp(cmdtext,"/car",true))
    {
        new Float:x,Float:y,Float:z;
        GetPlayerPos(playerid,x,y,z);
        CreateVehicle(560,x+2,y,z,0,99,99,-1,0);
        return 1;
    }
    return SendClientMessage(playerid, COLOR_WHITE, "[Server] That command dosn't exist.");
}