WCSession transferFile not doing anything

Hello,

I am trying to send data from a Watch App to an iOS companion app.

However when I call: WCSession.default.transferFile(file, metadata: [fileName:fileName])

nothing seems to happen, since

func session(
        _ session: WCSession,
        didFinish fileTransfer: WCSessionFileTransfer,
        error: Error?
    )

is never called on the delegate.

I have done all the necessary linking between the two apps, activated the WCSession.default and set the delegate in both, etc. I confirm the setup is correct by doing this series of checks before invoking the transferFile function:

func canSendMessages() -> Bool {
        /*
         We can only send messages if the WatchConnectivity Session is activated and the companion app to this app is installed
         */
        
        if WCSession.default.activationState != .activated  {
                return false
        }
        #if os(iOS)
        if !WCSession.default.isWatchAppInstalled {
            return false
        }
        #else
        if  !WCSession.default.isCompanionAppInstalled  {
            return false

        }
        #endif
        
        return true
    }

Has anyone run into this before / have suggestions to unblock?

Using watchOS 9.4