ALEXHD14 When encountering problems flashing GrapheneOS, most issues are caused by a bad cable or connection. I don't recall anyone ever reporting that error here before, so either my memory is going or it's very uncommon. It suggests that (I'm guessing) the connection is slow or the connection was lost. Did the phone restart and the browser asked for permission to connect to the device again? If not, I'd try:
- a different cable
- a different port
- maybe a different browser
- maybe a different device to flash from