Esp8266 firmware update with uno "chip sync error"
I run the same problem too and took me countless hours to figure this error out. The problem seems the Baud rate starts at 115200 while the COM port is set to 9600. What I did is I checked the Device Manager and find the COM port, right clicked to properties and to the Port Settings Tab, I changed the Baud Rate to 115200 and flash the firmware again. And it works!