This error typically appears when using specialized iOS management or bypass tools (like Broque Ramdisk iRemovalPro
If you are trying to go from iOS 17.4 back to 17.3, you will face this error if the "signing window" has closed. ecid not registered install
Connect your device -> Click on the Serial Number until it changes to "ECID." Right-click to copy. This error typically appears when using specialized iOS
Connect your device to a computer and open (macOS) or iTunes (Windows). Click on the device info section until the ECID appears. Copy the string of numbers and letters. ecid not registered install