How to fix iPhone with error iMessage not delivered ?
Image source: http://www.mod-gadget.com/imessage-down-delays-send-failures/
Only do this if your imessage send failure happens with no reason. You must be on Wi-Fi or 3G/LTE and make sure iMessage activated too. If iMessage already worked before then imessage stopped working suddenly, here is the guide to fix imessage not working issue.
1) Make sure iDevice is on
2) Goto Settings – Messages -Turn off iMessage
3) Hold down Power (Home) Button and Sleep button together until iDevice Shuts off
4) Take out Sim Card
5) Wait 20-30 Seconds
6) Put Sim Card back in
7) Turn on iPhone
8) Go to Settings → Messages → Turn iMessage ON
9) Wait for Activation
10) Once activation is complete you should be able to send messages again.
This works for iOS 6.1.3 + [ iOS 7 / iOS 7.0.2 ]
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