It is, let's say, tricky.
Maybe you on an old FW Version that need an Internet Connection to set the System Time, otherwise the verification failed.
See older Posts similar to this issue below:
Firmware 5.2.8 Update failed
Upgrade UL3 firmware from 5.2.8 to 5.2.11 from USB not working
5.2.11 Broke my WiFi on S5