If the health code turns black because it is still under review, you just need to wait patiently for a while, and the health code will be displayed normally after the review. If it is a black code caused by unsuccessful user authentication or failed authentication, it is recommended to re-verify the code. If the user does not use the health code for a long time and the black code is caused by network delay, it is recommended to log in again and refresh several times to return to normal.
Importance of health code
The color of the health code represents the user's own health status. If it is a green code, it means that the user is healthy and can pass normally. The yellow code and red team indicate that the user may be infected by COVID-19 at present, so he can't pass normally. If necessary, centralized isolation observation and treatment are needed, so if the health code turns black, they can't take the high-speed train at this time.