Error when obtaining certificate from Acme Staging API

[david-garcia-garcia]

8:53:05: System.AggregateException (uint)e.HResult=[2148734208] ErrorCode=
One or more errors occurred.
Aggregate Exception
  System.InvalidOperationException (uint)e.HResult=[2148734217] ErrorCode=
  An invalid request URI was provided. The request URI must either be an absolute URI or BaseAddress must be set.
     at Certify.ACME.Anvil.Acme.AcmeHttpClient.<Post>d__13`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Certify.ACME.Anvil.Acme.IAcmeHttpClientExtensions.<Post>d__0`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Certify.ACME.Anvil.Acme.OrderContext.<Download>d__3.MoveNext()
Inner Exception
  System.InvalidOperationException (uint)e.HResult=[2148734217] ErrorCode=
  An invalid request URI was provided. The request URI must either be an absolute URI or BaseAddress must be set.
     at Certify.ACME.Anvil.Acme.AcmeHttpClient.<Post>d__13`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Certify.ACME.Anvil.Acme.IAcmeHttpClientExtensions.<Post>d__0`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Certify.ACME.Anvil.Acme.OrderContext.<Download>d__3.MoveNext()

This happens when calling:

CertificateChain cert = this.OrderContext.Download().Result;

The exact same construct works using the Acme (non staging) API.

[webprofusion-chrisc]

Which CA are you using? As part of ACME the CA provides the URL of the cert to download. https://datatracker.ietf.org/doc/html/rfc8555#page-51