I'm 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).
Note that if you are issued a refund, your Flume Pro licence with become disabled and your access to Flume Pro's features will be removed from Flume. I offer refunds up to 30 days from your purchase date. Contact me with your purchase information.
Please note: If you paid via PayPal, please do not open a dispute via PayPal without attempting to contact me first. Once a dispute is opened, I cannot issue you a refund immediately and your refund will be delayed until PayPal closes the dispute in your favour (up to 75 days).
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. Note that when your Setapp subscription period ends or is cancelled, you will no longer be able to launch Flume via Setapp until you renew your subscription again.
Mac App Store Version
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.