Upload Attachment Not Associating to Document (requiring additional call)

We are trying to use the code below to upload an attachment to a document. I believe the ASsignDocument may be an extra call. The fact that we are setting the Document / Entity Reference seems like it should be attaching it on upload. See the code sample below. The last line seems unnecessary but without it, the attachment goes into the unassigned attachment bucket.

var newAttachment = new LoanAttachment(fileInfo.Name.Replace(fileInfo.Extension, "")
               , fileInfo.Name, AttachmentCreateReason.Upload);
           newAttachment.Document = new EncompassRest.EntityReference(containerId, EncompassRest.EntityType.Document);
           var attachmentID = await apis.Attachments.UploadAttachmentAsync(newAttachment,fileData);
           await apis.Documents.AssignDocumentAttachmentsAsync(containerId, EncompassRest.AssignmentAction.Add,
               new List<EncompassRest.EntityReference>() { new EncompassRest.EntityReference(attachmentID, EncompassRest.EntityType.Attachment) });
           

[leerodgers]

That worked!

[TylerBrinkley]

Could you try adding the following code before making your request?

attachment.ExtensionData["documentRefId"] = documentId;

If that works for you then we can add a strongly-typed DocumentRefId property to LoanAttachment.