I am unable to purchase items in vending machines with economics, I have the currency set as blood in vendingmanger but it says I cannot afford the item. when I reload Economics I get the following in console?

> o.reload Economics
[Economics] Saving balances for players...
[VendingManager] Economics detected - money purchases enabled
Loaded plugin Economics v3.4.0 by Wulf
Failed to call hook 'OnOpenVendingShop' on plugin 'VendingManager v0.2.6' (NullReferenceException: Object reference not set to an instance of an object) at Oxide.Plugins.VendingManager.OnOpenVendingShop (VendingMachine vm, BasePlayer player) [0x000e1] in <76d04a78e828481c9131d2921c01e05d>:0
at Oxide.Plugins.VendingManager.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00794] in <76d04a78e828481c9131d2921c01e05d>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0​

any idea what the issue might be?