The flash payment function is the secret-free function, and the specific opening method is as follows:

1. Open the China Bank application, find the "Account Management" option, and click Enter.

2. Select the card with flash payment function, and click Enter.

3. Click the "More" option in the upper right corner.

4. Find the option of "transaction limit setting" and click Enter.

5. Find the "Small/No Signature" option and click Enter.

6. Locate the Small/No Signature option, and then click Open.