G4S configuration is required in both Salesforce and .NET.
Salesforce
Follow the process of creating an API user, or editing an existing user, as outlined in the S4S documentation. You may need to change the names from S4S to G4S.
.NET
Your .NET application will need to be configured to use the connector against your Salesforce organization. G4S G4S has two modes of operation, running as an application and running in a web context. Configuration requires making manual changes to your .NET configuration file (usually web.config for websites/web applications or app.config for standard applications).
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