After upgrading iPhone 6 to 8.4.1, why can’t I send text messages?

Troubleshooting when iPhone 6 plus cannot send text messages:

1. Make sure the signal is normal and turn off airplane mode.

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.

5. If you send text messages to multiple people and enter the numbers manually, please make sure you press line feed instead of spaces to separate each number.

6. If you can receive but cannot send text messages, after the above problems are eliminated, you can use internal commands to edit the SMS center number.

Set SMS center number: Use iPhone to dial *5005*7672*+86 SMS center number#

Delete SMS center number: Use iPhone to dial ##5005*7672#

Query the set SMS center number: Use iPhone to dial *#5005*7672#

When using internal commands, first use the delete command and then set the SMS center number.

I hope the answer will be helpful to you