A non-offical and sane Bitpay API compatible client library created because the official project is barely usable.
You can reference the package with Nuget, and use the Bitpay class.
Please, check and run the NBitpayClient.Tests project, as a working example. For the example to work, you need a fully synched Bitcoin Core Testnet node, then modify your settings here for the test to work.
This project is under MIT licence.