SAML Authentication issue

Hello all,

We have configured OKTA set up in Appian and it was working fine for one month. But, from today morning we are seeing an issue while logging into Appian. Nothing has been changed either in Appian or OKTa.

The error message on the  SAML test configuration button is saying as "Assertion failed security policy check". When I am looking for a resolution in the Appian community I found the below solution. 

• Error: Assertion failed security policy check.
• Reason: The date-time of the Service Provider and Identity Providers do not match. Please check the server times on both the servers and make sure they are synchronized. Appian will check timestamps in SAML assertions to make sure they are not stale.Docs link: https://community.appian.com/support/w/kb/298/kb-1073-how-to-configure-saml-in-appian-7-11-and-later

We are hosting the Appian application on GCP. Where can I see the server's time setting and how can I make that changes.

And also, What could be the possible reason it was working earlier with the same configurations. 

Please help me to resolve this issue.

Thanks.