If you are using an eSIM (digital SIM) on an iPhone 14/15/16 or recent Galaxy flagship, the error isn't physical—it's software. US Cellular’s network occasionally fails to "re-authenticate" the handshake with your device. When the phone requests a refresh and the tower doesn't recognize the digital signature, it spits out the same "Invalid" message an old physical card would.
A simple reboot can refresh internal caches and reload SIM settings that may have hung.