Error: 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: TCP Provider, error: 0 - The wait operation timed out.) (Microsoft SQL Server, Error: 258)
The wait operation timed out
Understanding the Error
In order to understand the error, every scenario is different, you as a Software Developer has to know where the Database lives. Databases and Applications communicate over TCP, therefore, understanding a little bit about TCP would be really helpful to diagnose the issue.
It is possible that your Database Server is not set up to accept the remote connection using TCP Provider, the Database server is only listening to local traffic or traffic coming from a Private Network Adapter. Remember if you intend to allow remote access to the Database Server you have to take extra steps to secure the connection.