Annotation 'Odata.context' was not recognised

Ran into a similar problem when creating a draft message first using AddAsync() and then sending the message using SendMail().PostAsync(). It was resulting in the following exception: Message: Code: RequestBodyRead Message: The annotation 'odata.context' was found. This annotation is either not recognized or not expected at the current position.

I replaced the SendMail().PostAsync() with Send().PostAsync() and the problem was resolved. Code snippet below

            //Construct the Email Message
            var emailMessage = new Message
            {
                Subject = emailSubject,
                Body = new ItemBody
                {
                    ContentType = BodyType.Html,
                    Content = emailBody
                },
                ToRecipients = toEmailList,
                CcRecipients = ccEmailList,
                BccRecipients = bccEmailList,

            };

            //Create a draft message
            var draftEmailMessage = await graphClient.Users[emailId].Messages
                    .Request()
                    .AddAsync(emailMessage);

            //Code to add attachments to the draft message
            ....

            //Send the email message
            // NOTE: This does NOT work, throws Odata.context error 
            /*
            await graphClient.Users[emailId].SendMail(draftEmailMessage, true)
                .Request()
                .PostAsync();
            */
            // NOTE: Replaced above commented code with this - works perfectly!
            await graphClient.Users[emailId].Messages[draftEmailMessage.Id].Send()
                .Request()
                .PostAsync();