SQL Server:Login failed for user 'sa'. (Microsoft SQL Server, Error: 18456)

Sometimes you can connect to MS SQL Server Management Studio with Windows Authentication but is unable to connect with SQL Server Authentication. You might get the below error message:

Login failed for user 'sa'. (Microsoft SQL Server, Error: 18456)

The most probable reason for this could be that when you first installed SQL Server and configured, you might have set the Server Authentication mode to Windows Authentication Mode only. Follow the below steps to solve this issue.

1. Login to the MS SQL Server Management Studio with Windows Authentication. 
2. In SQL Server Management Studio Object Explorer, right-click the server, and then click Properties. 
3. In the Server Properties window, select "Security" under "Select a page" section. 
4. Select the Server authentication as "SQL Server and Windows Authentication mode" and click Ok. 
5. Restart the SQL Services and then try to login with 'sa' details.

Set Server Authentication mode to SQL Server and Windows

Restart MSSQL servies before trying to login again.