The full error:
Error - Could not establish connection to the database
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).
The cause of this issue is that the local computer cannot create a connection to the SQL server. This error could be due to one or a combination of the following;
the server is offline.
changes have been made to the internal network.
network connectivity issues on the local device.
the public-facing IP address that the user is given when connecting is not one of the ones permitted to access the SQL Server.
a network timing issue with the speed on the internet connection is just taking too long to connect.
The public-facing IP address can be checked by going to the following website on the user's laptop and also on the server - ip4.me.
The best way to resolve this issue is to set up the user to connect via a Remote desktop Session using Microsoft's RDP tools or a product like Citrix.