Xiaomi 6 can receive short messages, but can't send them by short messages. What happened?

1. Please open Settings ~ Application ~ Information ~ Clear Data to see if it is normal. It still doesn't work. Please insert your mobile phone card into other mobile phones to see if you can send and receive short messages normally. 2. If you can't send and receive SMS normally, please contact the network operator to see if it is a sim card problem. 3. If you can send and receive short messages, I suggest you plug the card back into your mobile phone and send yourself a short message to see if you can receive it. Please enter the SMS center and contact your mobile operator to check your SMS center number. 5. If the number is correct, please uninstall your system security software temporarily. 6. If it still can't be solved, please back up the data, enter Restore to clear the cache, user data and all data, and don't restore the system settings after entering the system. 7. If you still can't recover, please check at the maintenance point near you.