I am unable to access "Edit Metadata" from within a Google Doc (Add-ons menu). I'm confident I have followed the installation process correctly. I have installed Metadrive and created some custom metadata for some folders. I have also installed the Google Docs add-on. I can follow the steps in your You Tube video (
http://tinyurl.com/yao4wxqf) all the way up to 1:04. THat is where you navigate to Add-ons > Metadrive Add-on > Edit Properties. But in that menu, what I see is Add-ons > Metadrive For Docs > Update Metadata. If I invoke that, it opens a side panel that asks me to Create Folder Metadata (which I have already done). That just takes me back to the folder view (where I can see the custom metadata already exists).
Unfortunately, I won't be able to use Matadrive at all for our organisation unless and until this is resolved.