Apple appears to have stopped signing iOS 12.1.3 on Monday, a move on the Cupertino-based company’s part that prevents iOS device users from downgrading their device’s installed firmware from iOS 12.1.4 via iTunes.
This move doesn’t impact the jailbreak community very much because the latest jailbreakable firmware at the time of this writing is iOS 12.1.2, which Apple stopped signing more than a month ago. That said, the jailbreak community isn’t particularly rushing to downgrade to iOS 12.1.3 these days.
Apple had released iOS 12.1.4 in the first week of February so the company kept signing iOS 12.1.3 for an unusually long time.
Right now, with iOS 12.2 still not released, iOS 12.1.4 is the only release that is being signed by Apple. If you are looking to downgrade your iPhone or iPad to iOS 12.1.3 for some reason, it would only be possible if you had saved the required SHSH blobs. Otherwise, you are out of luck here.