I have an Unlocked Essential phone that I've have been using on other networks for almost a two years, and after a recent security update the phone has given me the"invalid sim" messageand I can't use it. The phone was working with the same sim card in it until the recent security update.
Howdy Jacksparrow. This sounds super frustrating, and I'll be more than happy to dig into for you. Where was the phone purchased? Was this device ever active on the Sprint network?