[Gustavob]

Silly me.

pawn Код:

CMD:changegravity(playerid,params[]){
    new Float:gravity, string[128];
    if(PlayerInfo[playerid][pAdminDuty] == 0) return SendClientMessage(playerid,COLOR_GRAY,"Error: You're not on admin duty!");
    else if(PlayerInfo[playerid][pAdmin] < 4) return AdminRefuse(playerid);
    else if(sscanf(params,"f",gravity)) return SendClientMessage(playerid,COLOR_GRAY,"Syntax: /changegravity [gravity]");
    else
    {
        format(string,sizeof(string),"Admin %s has set the gravity to %f",GetName(playerid),gravity);
        SendClientMessageToAll(COLOR_YELLOW,string);
        SetGravity(gravity);
    }
    return 1;
}

That should do it. Just added SetGravity(gravity) inside the last else, which was missing for some reason.