If you have purchased a second-hand B311-221 or switched to a cheaper data plan, you have likely hit the dreaded "Invalid SIM" or "SIM Lock" message. The solution is not a new router; it is the .
: While some forums and Google Drive links claim to offer "unlock firmware," use these with extreme caution. Installing unofficial firmware often requires specific hardware tools (like a USB-to-TTL adapter) and may void your warranty. Unlocking Steps (with Code)
Power on the router and connect your computer to it via Ethernet cable or Wi-Fi.
The primary feature is the ability to use nano-SIM cards from any global network provider.
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