Email srijanbuildsconnect@gmail.com — replies usually within two working days. For bugs and questions you can also open an issue at https://github.com/srijan-kaiwart/flow-connector/issues (public, so never post your payment email there).
Pro members also get WhatsApp support: from version 1.2.6, open the extension's Help tab and tap "Chat on WhatsApp". Messages only — calls are not answered.
Before you write, the Help tab inside the extension has a "Report a problem" button that fills in your version, browser and recent log for you. That information is what makes a problem fixable, so using it saves a round trip.
This is a one-person project. Support is best-effort, and a reply usually comes within two working days.
Flow Connector is operated by an individual proprietor based in Chhattisgarh, India. Full registered details are provided to payment partners and are available on request.