Failed to open serial port: Permission denied

This error message typically indicates that the user does not have permission to access the serial port.

To fix this issue, try the following steps:

1. Check if the serial port is currently in use by another application. If so, close that application and try again.

2. Check if you have the necessary permissions to access the serial port. On Linux, you may need to add your user account to the dialout group. On Windows, you may need to run the application as an administrator.

3. Try unplugging and plugging in the serial device again, and make sure that it is connected properly.

4. If none of the above steps work, try restarting your computer and attempting to access the serial port again.

If the issue persists, it may be a hardware problem with the serial port or device, and you may need to contact the manufacturer for support.