Xojo.Net.HTTPSocket no credentials were available in the client certificate

I’m trying to connect to https://api.nitrado.net/ in Windows 10 with Xojo.Net.HTTPSocket and I’m getting a “no credentials were available in the client certificate” error. There’s no error number included. Or, it’s an overloaded integer, so there might as well be no error number.

Anybody have any idea what this is about? Google has not returned any useful results and since I don’t have an error number, I can’t match up the error to https://docs.microsoft.com/en-us/windows/desktop/WinHttp/error-messages with any confidence.

Correction, the error number is not an integer overflow. It’s -2147012711 ERROR_WINHTTP_CLIENT_CERT_NO_PRIVATE_KEY. Still, I’m not sure the solution.