Resona Pro in a minute.
A license is tied to one Mac: paste its Mac ID, pick a plan and pay. Pro switches on by itself.
1. The Mac ID from the app
In Resona open Settings → Plan → “Upgrade” (if Pro is already on, “Open” next to “Mac ID and key”): the window shows the Mac ID with a “Copy” button. Paste it here.
Not installed yet? Download Resona; it is free, and Pro can be bought later inside the app.
2. Plan
3. Payment
After paying you get a page with your key and “Open in Resona”; Pro switches on by itself. The key is tied to this Mac. You can turn auto-renewal off at any time: in the app (Settings → Plan) or on the auto-renewal page.