Recently, our firmware server has improved the security level by using HTTPS protocol.
For old products like U-Series, Gateways are not able to use HTTP way to upgrade
as they don't support to download by HTTPS links.
To ger rid of the trouble, we suggest to our users to download the firmware first, then use TFTP way to upgrade.
Go to the page to download firmware file (*.bin) first:https://www.yeastar.com/firmware-download/
Then follow the Method 2 - TFTP in the article : https://support.yeastar.com/hc/en-us/articles/217745237-How-to-Do-Firmware-Update
As for system prompt, you could use the TFTP method in this article: https://support.yeastar.com/hc/en-us/articles/217451767-Update-System-Prompt