SQL Server Connected system OAuth2.0 Test failure

My guess, The issue is the SQL Server database user for the service principal (Client Id)is not created or lacks permissions.

Try below links for reference
https://learn.microsoft.com/en-us/azure/azure-sql/database/authentication-aad-service-principal?view=azuresql
https://learn.microsoft.com/en-us/sql/connect/jdbc/connecting-using-azure-active-directory-authentication?view=sql-server-ver17
https://docs.appian.com/suite/help/25.3/setting_up_an_oauth_connected_system.html
https://docs.appian.com/suite/help/25.3/Configuring_Relational_Databases.html#sql-server

There should be a more concise error in System Logs > tomcat-stdOut.log. Could you post that exception here? Without a more concise error, we're guessing about many variables related to your Appian configuration and where your database lives.

IF your database is in Azure Cloud, also check these:

• On a different project / platform, AzureTenant JDBC property needed to be added to the JDBC connection string for a Teams integration that also used ServicePrincipal. I'm not sure if that applies to your situation, but it's pretty easy to test.
• Appian might have additional VPN requirements depending on your environment's configuration:
  docs.appian.com/.../Microsoft_Azure_DB_Integration_Appian_Cloud.html

Check logs please and share the error...

I already tried to find the error in logs but could not obtain anything specific.

2025-09-25 01:36:31,065 [Appian Timer - 1] WARN com.appiancorp.common.ObjectSynchronizer - 1 services were missing users.
2025-09-25 01:36:57,229 [pool-109-thread-1] INFO com.appiancorp.oauth.inbound.authserver.tokens.TokenFamilyMaintenanceRunnable - Starting OAuth Token Family table maintenance...
2025-09-25 01:36:57,232 [pool-109-thread-1] INFO com.appiancorp.oauth.inbound.authserver.tokens.TokenFamilyMaintenanceRunnable - Finished OAuth Token Family table maintenance.
2025-09-25 01:40:17,842 [Appian Timer - 3] ERROR com.appiancorp.common.monitoring.AbstractLogScheduler - Error logging for class com.appiancorp.object.versions.monitoring.DesignObjectVersionMetricsLogScheduler
com.appiancorp.suiteapi.common.exceptions.AppianException: Invalid Type: {www.appian.com/.../2009}TranslationString (APNX-1-4047-000)

Can you replicate this configuration for example via postman and check if it works?

hi Sure.

Hi,
There was an IP whitelist issue on the firewall and we got it fixed to ensure the VPN tunnel connectivity. 
however, a new error is being faced saying invalid credentials. Internally, we are able to use the same service principal successfully. not sure what could be done next. 
The logs shows the below error: 

2025-09-29 18:44:13,781 [ConnectionTimeoutBasicDataSource-0] INFO  com.appiancorp.connectedsystems.http.oauth.HttpOAuthTokenRetriever - Error while retrieving token: unauthorized attempting to pass Authentication in body
2025-09-29 18:44:13,950 [ConnectionTimeoutBasicDataSource-0] INFO  com.appiancorp.connectedsystems.http.oauth.HttpOAuthTokenRetriever - Error while retrieving token using auth in body: unauthorized

Client Id, client secret, or token endpoint is incorrect or the OAuth credentials are not sent as parameters in the request body exactly as expected.