MS SQL Server 2019 Trouble Shooting

I need someone urgently to help trouble shoot some MS SQL Server 2019 issues we are facing currently. We have a DB server and an Applications Server and the Application server is unable to make a connection with the DB server. A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 1326)

We feel we have gone through all the trouble shooting steps but looking for expert help to resolve this quickly.