I also have the unlocked s7 edge purchased from Samsung 4/10/2017 with the exact same issue. I use Tracfone with Verizon service. When phone was purchased it had Android 6, did update to Android 7 in May. On 6/9/2017 Samsung did a system update for Android 7. That's when this issue started. Now any sms text message is sent, it displays the working circle next to text. The message is sent almost immediately but the working circle contiues for about a minute or two and then displays failed to send, with options to resend, edit or cancel. Very frustrating to continue to receive failed to send messages. I changed sim card to try a Tmobile and messages would send normally using GSM network. There seems to be a software issue with these phones using Verizon service. Sent my phone to Samsung for factory service. They changed some internal components and sent phone back. There repairs did not correct the problem. Still continue to receive failed to send error messages.
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