A message that shows "Not sent. Tap to try again." didn't leave the phone. Tap it to send it again.
Common causes:
- No signal or airplane mode on.
- No credit on a pay-as-you-go SIM, or texts to that number or country not included in your plan.
- The wrong SIM on a dual-SIM phone: Android sends texts from the SIM chosen for SMS in Settings → SIM cards (or Connections → SIM manager); pick the SIM that has credit.
- A wrong number, for example without the country code when texting abroad.
Long messages are sent as several SMS: the counter in the text box shows how many characters are left and how many SMS it takes.
1krBlocker sends messages the same way any SMS app does; checks only apply to messages you receive.