Trouble with updating a row in mobile client then syncing - xamarin.android

Question

Problem: Trouble with updating a row from the mobile client (with offline sync).
Scenario: We're using a Class in the mobile client to save new items. But we're using a ClassDto when retrieving data from the server. Because of this setup, the server backend has two table controllers: ClassController:TableController<Class> and ClassDtoController:TableController<Class>. The former is used for the PostClass requests and the latter is used for the GetAllClass requests.
On the client side, the mobile database stores the rows for viewing in the ClassDto local table and only the saved entries using the mobile device are in the Class local table (i.e. ClassDto entries count != Class entries count).
Problem Detail: We need the capability to edit a Class using the device. We implemented this by copying all the (edited and unedited) details of the target ClassDto (e.g. id, version, updated at, created at etc) into a new instance of Class then used UpdateAsync on the IMobileServicesSyncTable.
From the logs in the ClassController:TableController<Class>, the request goes to this table but an error occurs.
Used a try-catch to expose the exception and this is what we got:
Message: "Processing of the HTTP request resulted in an exception. Please see the HTTP response returned by the 'Response' property of this exception for details."
Stack Trace:
at Microsoft.Azure.Mobile.Server.Tables.EntityUtils.<SubmitChangesAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Azure.Mobile.Server.EntityDomainManager`1.<UpdateAsync>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Azure.Mobile.Server.EntityDomainManager`1.<UpdateAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.Azure.Mobile.Server.TableController`1.<PatchAsync>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at SynthesisServer.Controllers.SaleController.<PatchSale>d__3.MoveNext()
Used PostMan to do a patch and got this message:
{
"message": "An error has occurred."
}
Question: How do we implement the editing function? Also, is it possible to use only one Table Controller for both saving and retrieving entries? We used two controllers cos can't do joins in the mobile client. We tried returning a ClassDto from the ClassController but that resulted to an error. We also tried pushing a ClassDto to the ClassController but that again resulted to an error.