Apple 1 1 Why can't the secondary card send text messages?

Apple 1 1 uses the secondary card to send short messages as follows:

1, first go to Apple's1/mobile phone desktop and find the green dialing icon below. Click on it;

2. Click Address Book in the bottom menu bar;

3. Then find the contact you want to call and click on it;

4. After entering the contact details page, click the main number under the contact name;

5. Then you can see the primary and secondary number options in your phone, click Switch, and then send a message.

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