What's going on when Apple's iPhone 7 fails to send messages and prompts "Message sending failed"?

1. Is the mobile phone signal normal?

2. Check whether the SIM card status is normal.

3. Check whether the send button is bright and clickable.

4. If you cannot click send after entering text, the "Send" button will still be gray and cannot be clicked. Please go to Settings > SMS > turn off "Show subject bar".

5. If it is a group text message and the numbers are entered manually, please make sure to use line breaks instead of spaces to separate each number.

6. After the above problems are eliminated, you can first check whether the SMS center number of your mobile phone is correct. If it is incorrect, you can delete it and then reset it. After setting it, you can also check again whether the SMS center number is correct.