I found a way to purchase 1Password 7 directly from the reseller, without requiring the app installed. (in-app)
The in-app purchase feature does use a web-api service of the reseller, which can be access directly with a browser. So I don't understand why agilebits hides this information or insists on in-app purchase option only.
These are the links, just tested for both Windows and Mac:
1Password Version: 7.0.4
Extension Version: Not Provided
OS Version: OS X 10.13.4
Sync Type: Dropbox