My galaxy s7 (flat) upto date as of April 24th 2018 has been having texting troubles for months. On cellular with anywhere from 2 to full bars (I tested in multiple places.) Every time I try to send a text message it fails once or twice requiring me to manually resend it. After that for the next five minute or so my texting works as normal and then it restarts the issue. It is repeatable on the stock messaging app or on textra. Also wifi texting has never worked for me, on any wifi network (public, private, etc) and I have tried airplane mode and areas with no reception.