Why do I use QQ on my mobile phone to send text messages for verification?

Because the qq device lock has been opened.

Qq device lock closed:

1, open mobile QQ, enter settings and find the device lock.

2. Select to close the device lock, as shown in the figure below.

3. Confirm to close the equipment lock, as shown in the figure below.

You can turn off the equipment and turn it on when you need it next time. You don't need to verify the device when you turn it on again, as shown in the figure below.