How to set Samsung mobile phone to automatically reply to SMS when no one answers the phone?

According to your description: the mobile phone can't send information automatically when no one answers.

When the phone calls, there is an option of "Reject the call and send a short message" at the bottom of the screen. You can click and drag to the screen of the mobile phone, choose to refuse to answer the short message, refuse to answer the phone according to the prompt and reply to the short message. Add the content of rejection message: standby-mobile phone-menu key-call setting-set rejection message (maximum 6).

Or I suggest you check whether the third-party software can realize this function.

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