[Konstantinos]

You can't use it inside any callback.

pawn Код:

public OnPlayerCommandText(playerid, cmdtext[]) 
{
    return 1;
}
// Outside
CMD:fbi(playerid, params[])
{
    if(GetPlayerSkin(playerid) != 280 && GetPlayerSkin(playerid) != 281 && GetPlayerSkin(playerid) != 282 && GetPlayerSkin(playerid) != 283 && GetPlayerSkin(playerid) != 284 && GetPlayerSkin(playerid) != 285 && GetPlayerSkin(playerid) != 286 && GetPlayerSkin(playerid) != 287 && GetPlayerSkin(playerid) != 288)
    {
        ShowPlayerDialog(playerid, 1123, DIALOG_STYLE_LIST, "So you want to have a SPU, what one do you want then?", DIALOG1_MSG, "Take it", "Leave it" );
    }
    else
    {
        SendClientMessage(playerid, COLOR_RED, "You need to be in the Police Force to beable to use this.");
    }
    return 1;
}