If you are trying to optimize RAM, ignore the serial number field. If you bought a physical tiny screen, look at the sticker on the back of the device.
The Mini Monitor is available in both free and Pro versions. A significant advantage for users is that the free version contains . However, purchasing a serial number for approximately $4.99 unlocks the Pro features. Free Version Features: Basic memory usage display (percentage, commit total). Global hotkey support to manually trigger cleaning.
If you absolutely refuse to pay for a serial number, there are free alternatives that replicate the Mini Monitor experience: