Read the failed bubble first: blue uses iMessage, while green uses carrier messaging or RCS where supported. Tap the red exclamation point only after checking connectivity, the destination, and whether Send as Text Message is appropriate.
Do not delete the conversation first. Keep the failed bubble, time, recipient, and exact alert because they show whether the problem is Apple’s iMessage service, the mobile carrier’s messaging path, or one destination.
Classify the failed message
A blue bubble is iMessage and needs internet plus an activated sending address. A green bubble uses SMS/MMS or RCS where the device and carrier support it. Open Settings > Apps > Messages and verify that iMessage is on, Send & Receive shows the intended phone number or Apple Account address, and the mobile line is enabled.
Check Apple’s System Status for iMessage if every blue message fails. For green messages, confirm cellular service and contact the carrier about account-level SMS/MMS or RCS provisioning, especially after changing carriers, eSIMs, or phone numbers.
Read the red-exclamation options carefully
Tap the red exclamation point. Try Again repeats the same route. Send as Text Message may be offered for a failed iMessage, but it can use the carrier plan and is not appropriate for every international or premium destination. Verify the recipient before switching routes so a message is not sent to the wrong number.
For a photo or group thread, confirm MMS Messaging and available data. A plain one-to-one text that works while a group photo fails points to a media or group-messaging condition, not a total Messages outage. Restart the iPhone and install supported carrier-settings and iOS updates.
Protect the conversation and escalate with evidence
If only one person fails, start a new message by manually selecting the correct current number or address. Do not keep an old contact thread that routes to a retired number. Ask the recipient through another channel whether they recently moved between iPhone and Android.
Success is a delivered indicator for iMessage or the absence of the failure alert for carrier messaging, followed by a reply from the intended person. If failure continues, give Apple or the carrier the bubble color, alert text, timestamps, affected destinations, line status, and whether calls and cellular data work. Never post message contents or verification codes publicly.
Primary sources
Interfaces and policies change. We recheck the steps above against these sources and show the verification date at the top of the guide.