6s suddenly can't send text messages, but it can be sent to Unicom operators, and other contacts haven't sent them yet.

There may be the following reasons for not sending SMS:

1. There is a problem with the number setting of the SMS center. It is recommended to check whether the settings are correct.

2. In case of congestion caused by the peak sending volume of short messages during holidays, it is suggested to try again later or avoid the peak sending time;

3. The sending format is incorrect. If you send short messages to foreign users, you need to add the international access code and country code before the number, and then add the other party's number;

4. Check whether the SMS inbox and sending box are full;

5. Inquire whether the SMS function is enabled on the mobile phone card;

6. Check whether the signal at this position is normal. If the signal is weak or there is no service, there will also be cases where SMS cannot be sent.

If the above situation is still unresolved, it is recommended to contact Unicom customer service.