Can t send text message. Keep getting red exclamation. iPhone

There is necessary to have valid "cellular"or "WiFi" data connection  for to send and receive " i Messages". So to fix this issue try to basic Troubleshooting that is follow below : * WiFi networks and connections check. * Your  cellular data . * Your i Message is turned "ON" condition or not , if not go to "settings" and then tap to "message" option. * Your i Message registration should be validates for using  i Message application. * Verify that the "Caller ID" is correct in "Settings" >>  "Messages" >>  "Receive At" >>  "Caller ID". * After that "press" and "hold the Sleep/Wake" until the Apple logo appears then try to send your message again .It will work again OK

hope the answer for dah question