The sudden absence of Phnom Penh in the health code is due to the excessive system traffic, which leads to the temporary disappearance of Phnom Penh. Users can try to refresh many times, or wait a few days for Phnom Penh to appear again. Phnom Penh will not appear until all reagents of COVID-19 vaccine are inoculated, so Phnom Penh will not appear immediately after inoculation, and it will take several working hours. Health codes are based on actual data and can be generated by citizens or people who have returned to work through online declaration and background audit. As an individual entering and leaving electronic certificate locally, the QR code can be declared once, which is universal in the whole city. The introduction of the health code aims to make the work of returning to work more accurate, scientific and orderly.