The reasons for the failure of identifying the travel code are as follows: 1. The screenshot of the travel card is cut. 2. The font of the mobile phone is changed due to the theme setting of the mobile phone. 3, other unknown reasons failed to upload many times.

Travel code is a code of communication big data travel card, which is also equivalent to health code. It is a free inquiry service for 1.6 billion mobile phone users in China, which is obtained by China ICT Institute in conjunction with three basic telecom enterprises, namely China Telecom, China Mobile and China Unicom, using the data received by mobile phones, and through the location of the base station where the users' mobile phones are located. Through the service, mobile phone users can inquire about all the cities and cities they have visited in the previous 14 days.