Pinduoduo's mobile phone number is untied. Why can't I change it?

Pinduoduo can't unbind the mobile phone number, but it is ok to change the bound mobile phone number after binding. The method is as follows:

Demo version number Pinduoduo 6.22.0

1, first open the Pinduoduo, and then select the personal center as shown in the figure below:

2. Then select the settings as shown in the figure below:

3. Then select the bound mobile phone number, as shown in the figure below:

4, and then select the binding to change as shown in the figure below:

5. We enter the verification code here, and then click OK.

6. Finally, we just need to enter the replacement mobile phone number and then enter the verification code, and click Bind Now.