Where can I locate the serial number? GVIDO MUSIC Customer Support January 04, 2023 12:03 Updated It is listed on the microSD card tray. Related articles Who should I contact when I need technical support for GVIDO product? How to modify the PDF page size/DPI: What is the Support Center's operating hours? What is your return policy? When I try to register a seond hand GVIDO that was given or purchased in My Library, the message “This GVIDO is registered by other user” appears.