After flashing the firmware on the EX5501, the password is incorrect.

After flashing the firmware on the EX5501 (via serial connection), I can’t log in to the web interface; it shows a password error. I also can't access the serial command-line interface. I've tried common username and password combinations, such as admin/admin, admin/1234, etc., but none of them work. I'm considering looking for clues in the firmware I flashed. Do you have any suggestions?