The Reliability Ruse: What's Behind iMessage's Erratic Behavior? The iPhone's Messages app is designed to make staying in touch effortless, but the "Not Delivered" error has been a persistent issue for years.
This problem stems from the complex interplay of multiple services used by iMessage, including RCS and SMS protocols.
The Complexity Conundrum iMessage's reliance on these three services creates challenges for Apple when it comes to identifying and fixing issues quickly.