We're sorry to hear that Flume Pro did not meet your expectations. In most cases, the issues for requesting a refund are often resolvable through access to a pre-release version (in the case of a bug or error).
Mac App Store
Sales on the App Store are between you and Apple. As such, you must request a refund from Apple directly. Please note that refunds are only possible within 14 days of your Flume Pro purchase, as per Apple's refund policy.
We offer refunds up to 30 days from purchase date. Contact us with your purchase information.
There is no possibility to refund subscription fees for users using Flume for Mac via Setapp. Please see Setapp's support site for more info.