If the official update fails repeatedly, register 0x5A (BOOT_FLAGS) can be set to 0x01 to force recovery mode over TFTP.
If the registration portal repeatedly rejects your submission details, it is usually caused by an unstable server connection or an unvetted email format. Try switching your connection from local Wi-Fi to mobile data, or register using a mainstream provider like Gmail to ensure the automated verification messages bypass aggressive spam filters. Missing Verification Mail Htv 3.7.1 Register