The API BaseUrl should be changed from app.billbee.io to api.billbee.io, as advised by Dirk from Billbee Support. [ApiConfiguration.cs](https://github.com/billbeeio/billbee-csharp-sdk/blob/master/Billbee.Api.Client/ApiConfiguration.cs#L28) 
The API BaseUrl should be changed from app.billbee.io to api.billbee.io, as advised by Dirk from Billbee Support.
ApiConfiguration.cs