Server SSL certificate could not be proven ,Its security certificate is not trusted by the device ..

[Suhap]

Server SSL certificate could not be proven ,Its security certificate is not trusted by the device

Teams Native Phone 

Failed to connect to sfb server sipfed0A.online.lync.com

[#2]

SSL certificate errors can occur if the device doesn't have the correct time and date set, since it thinks the certificate is outside of its validity period. Have you confirmed that the phone is able to reach whichever NTP service it is configured to connect to?

[#3]

The Phone has the correct time..
I am seeing this issue for all the Teams Native Phone

[#4]

Have you made sure that there are no proxies or SSL interception devices interfering with the connection?

Have these phones ever worked on this network? If so, what has changed since then?

[#5]

@RyanSteele-CoV 

This has worked and there is no functionality issue but these errors are there since changes made for Certificate Authority by Microsoft 

[#6]

@Suhap If you are referring to the change documented at TLS certificate changes to Microsoft 365 services including Microsoft Teams - Microsoft Community Hu... that happened back in 2022, that did not have had any impact on Teams Native phones, as the new root certificate is already trusted by Android. Of course, you should ensure that your devices are running an up-to-date version of the firmware.