[Mattakil]

your indentations gave me a stroke.

pawn Код:

if( (

should only have one bracket.

(I fixed that and changed the indentations so I can read it better for more issues)

pawn Код:

if(ServerInfo[AdminOnlySkins] == 1)
 {
    if(GetPlayerSkin(playerid) == ServerInfo[AdminSkin])
    {
        if(PlayerInfo[playerid][Level] >= 1)
        {
            SetPlayerHealth(playerid, 100);
        }
        else
        {
            if(PlayerInfo[playerid][Level] >= 0)
            {
                SendClientMessage(playerid, red, "You are not an admin to use this skin");
            }
        }
    }
    return 0;
}

Though your code doesn't make sense, what are you trying to do