Dear TP-Link Support Team,

I am writing to seek urgent assistance regarding a critical issue I am facing with my TL-MR6400 (EU) modem. Recently, I attempted to update the firmware to the latest version, 1.5, but encountered a problem where the SIM functionality ceased to work. In an attempt to resolve this issue, I tried reverting to a previous firmware version; however, despite the system indicating a successful rollback, the modem still retained the problematic version 1.5.

Subsequently, I opted to try the beta firmware version 1.6 in hopes of resolving the SIM functionality problem. While the update process appeared to be successful this time, unfortunately, the issue persists, and the SIM functionality remains non-functional.

The current state of the modem renders it unusable, constantly displaying "error code 1." Given the critical nature of this problem and the urgency of restoring functionality to my modem, I kindly request your assistance in resolving this issue.

Could you please provide guidance on how I can effectively revert to a stable firmware version that ensures the proper functioning of the SIM card? Additionally, any insights or troubleshooting steps you can offer to rectify the SIM functionality issue would be greatly appreciated.

Thank you for your prompt attention to this matter. I eagerly await your response and assistance in resolving this critical issue.

Best regards,
Fabio