Auto Provision Wall Paper Stopped Working

[TRP Tech]

Well, we are getting closer. Yealink support was very helpful in determining the issue is being caused by an expired SSL certificate. I guess Lets Encrypt provides SSL certificates and they made a change on September 30th. Not sure why we didn't notice until now but because of that change, Yealink phones, especially ones with older firmware, can no longer access sites using HTTPS.

Yealink support suggested adding this to my config file...
static.security.trust_certificates="0"

It is interesting - adding that to the config file allows the phone to access the HTTPS site and download the wallpaper - but the phone won't set the downloaded file as the wallpaper until I reboot the phone. Not exactly sure why. If anyone has ideas on this new (but related) issue, I am all ears. Thanks in advance for any help.