I think the trailing comma at the last line is not allowed in JSON. And you need to use https://raw.githubusercontent.com/markus7017/myfiles/master/shelly/org-openhab-binding-shelly-4.3.0-dev.json, otherwise you won’t get the content of the file but the web view version.
but if I open the Addon-Store and filter for “Shelly” I only see the official binding and the beta one, but not my DXEV build.
Is the maturity “beta” valid? or is it “unstable”?
Is “org-markus7017-binding-shelly” a valid und? or do I have to use “org-openhab-binding-shelly”
Everything is valid as maturity, but everything except stable will not be shown when the switch is disabled. All UIDs are allowed, the only requirement is that they are unique within a marketplace type (i.e. no second add-on is allowed to have the same UID in all used JSON marketplaces).