TS-428 firmware download

I bought my QNAP TS-428 few years ago and its firmware version is 5.0.0.1891. It seems the signature is out of date.
Now I am going to upgrade my TS-428 to some new firmware version. Unfortunately I cannot find TS-428 in the download center.
What happened to TS-428? What can I do to upgrade its firmware?

Thanks much!

I think that’s a China exclusive model…did you check the Chinese download section?

When you press “Check for Update” from the firmware update page, what message is displayed?

Would you be able to provide a screenshot? That would be a great help. Thanks!