Refund of an app that doesn't work with Apple update

I downloaded an app ("Blotter") for my macbook on the 4th of May this year. However, with the new "macOS Big Sur" upgrade, this app no longer works. I contacted the company and they told me that it will be a while before they fix the app to work on the upgrade and they suggested I should request a refund. However, I can't see far enough back in my purchase history to request the refund (it only shows payments up to last month that I can request refunds on). How do I get this refunded? Thanks