What's the reason why Apple doesn't display primary and secondary numbers when texting?

Apple doesn't display the primary card and the secondary card in the short message, because the information content has not been edited. Only after editing the content can you select the primary card and the secondary card on the SMS content editing page. The operation method is as follows:

Tools: iPhone 1 1

Operating system: iOS 14.4. 1.

1. First click the information on the iPhone interface, as shown in the figure below;

2. Click the Create button in the upper right corner, as shown in the figure below;

3. Click the "Main Number" button, as shown in the figure below;

4. Select the secondary number from the following dialog box, as shown in the figure below;

5. After editing, click Send to send a message with the secondary card, as shown in the figure below;