I purchased the app from app store. When I click upgrade it says no purchase information found.
There is no direct entry for MarginNote(the cheaper essential/lite version) on Mac to upgrade to MarginNote 3. The default entry is for MarginNote Pro.
But there is a solution fixing that with just one extra step.
1.On Mac AppStore, please upgrade your 2nd-gen MarginNote to the MarginNote Pro version.
2.Once that is done, download MarginNote 3 and do the upgrade. It will by default jump to your MarginNote Pro app verifying installation status and purchase history.