If the flashing does not work properly, check these points:
1) Disable any anti-virus, firewall or anti-malware on the computer used for flashing. Flash programs can be considered malware depending on the computer. However, this is not the case with the machine’s flash program.
2) Make sure that you choose the COM port corresponding to the machine and not to another device present. (Unplug the machine to see if this port is still present or not in the list. This indicates that it is the one on the machine).
3) Try with another computer to be sure that the blockage does not come from this one. (Favour a computer with a recent OS, Win10+ natively supports the machine, no need for drivers)