As an addition. The main issue seems that the ServerPanel doesn't close after buying or selling from the integrated ServePanel UI Shop. It seems the global variable _enabledServerPanel is not true in any case.
I just changed
if (_enabledServerPanel) ServerPanel?.Call("API_OnServerPanelCallClose", player);
To
ServerPanel?.Call("API_OnServerPanelCallClose", player);
And also added this under private void CmdConsoleShop(ConsoleSystem.Arg arg) in case "sellitem"
ServerPanel?.Call("API_OnServerPanelCallClose", player);
_config?.Notifications?.ShowNotify(player, SellNotify, 0, totalAmount, item.GetPublicTitle(player));