Great plugin! Who have the same problem as me, when you click on the deposit or withdraw icon in the gui the gui closes.
This is how you can fix it:
1. Put the plugin in plugins folder, and start server
2. After config generated search the plugin folder and edit the "itemManager.yml" file
3. Search every "SIGN" word and replace it with "OAK_SIGN" (there are two of them)
4. Restart server or use /lb reload
After this the gui works perfectly for me on Spigot 1.15.2 :D
I hope this helps
Hope the developer and his friends or his own acconts (not sure) all from Israel (coincidence xD) don't review this resource with 1 star like the last time, haha. Big L to the developer that tried to add anti-leak to the plugin haha. Without a doubt