Apple closed the signatures of iOS 11.4.1. It is not possible to downgrade from iOS 12
Following the release of iOS 12.0.1, which took place yesterday evening, today Apple has blocked the signatures of iOS 11.4.1 that can no longer be installed.Also downgrade is not possible anymore to this version of the firmware. Now the only version that can be installed is iOS 12, or the new iOS 12.0.1,...