How does WP specify the number of contacts to send SMS?

You can enter a message directly, then select the cross symbol below to create a new one, and then press Add in the upper right corner to find the contact person who needs to send a message and select the number that needs to be sent. Another way is to find the contact person first, choose to send a message, then choose the switch in the lower right corner, choose more phone numbers, and finally choose the number to send.