A common search is "ZTE B866V2 unlock link for SIM." The B866V2 is generally a Fiber ONT. It does not have a SIM card slot for 4G. If your device has a SIM slot, it is likely a different model (like the ZTE MF286 or MF283). Do not use fiber unlocking methods on cellular routers; you will brick them.
There are three technical reasons a simple link doesn't work for the B866V2: zte zxv10 b866v2 unlock free link
Since firmware links change frequently, these creators and forums are the most reliable places to find active download links and step-by-step visuals: XDA Forums : Search the ZTE ZXV10 B866V2 A common search is "ZTE B866V2 unlock link for SIM
Community members often share firmware and tools on forums like Reddit and Facebook . zte zxv10 b866v2 unlock free link