Hi there,
we will start a western season and so there will be no vending machines, but some shopkeepers. 
I installed monument finder (all monuments are custom made and have monument markers) and Custom Vending Setup. I granted permissions and /mf finds all the monuments/monument markers. But there is no EDIT-Option for the shopkeepers. Is it not possible to use the plugin with the entity Shopkeeper VM invis?

Thanks in advance

Yes, it is possible to use with custom monuments and with invisible vending machines (works at the fishing village for example).

From the described symptoms, the vending machine is outside the bounds of the where Monument Finder thinks the monument is. Did you configure the bounds in Monument Finder? Can you run the "/mf closest" command while standing in front of the vending machine and take a screenshot? That will draw a box at the Monument representing its bounds. That is basically what CVS is calling to determine which monument the vending machine is closest to.

Thanks a lot. Meanwhile I found out how it works (MonumentFinder + MonumentAddons + CustomVendingMachines). Unfortunately, if you want to sell the same Item with different skins, the first skin is shown for all items, so you have to use different shopkeepers, but hey, thats ok.