[font="Courier New"]Hi,
Welcome to sqlservercentral 🙂
Make sure SQLserver port is unblocked in firewall
Make sure to create correct alias in the client machine
If possible try connecting as SERVERNAME,Portno Eg.)mymachine,1433
If you are using ODBC connection inside the app connection, test the odbc connection string
Try connecting the same using sql client tools[/font]