Getting unauthorized error when calling api's

Hi Team,

I’m using GitHub - EventDay/ A C# Wrapper around the API SDK for calling infusionsoft API , using OAuth() for authentication which is working fine.

But getting null API key in below method or when passing the hard coded API key getting unauthorized error.

protected ServiceBase(IInfusionSoftConfiguration configuration, IMethodListenerProvider listenerProvider)
MethodListenerProvider = listenerProvider;
Configuration = configuration;
_proxy = new InfusionsoftProxy(configuration, listenerProvider);
ApiKey = configuration.GetApiKey();
Please see below reference

My requirement is just to add a tag in infusionsoft contact using API.

Please help me to get out of this.

Thanks, Sonam