Sequence contains no matching element error on file upload - acumatica

Question

I have a custom screen, and I am using the REST API to upload a file. This was working correctly, but after the upgrade to 21.203.0030, it stopped working (error included below).
I have been trying various things such as re-creating the web service endpoint from scratch etc, but no luck.
It seems that Acumatica manages to add the file to the the UploadFile database table, but it is not being added to NoteDoc (which I believe acts as the link between the screen and the attachments)
Would anyone have any suggestions on what I could try?
ERROR:
System.ApplicationException: File Upload - {"message":"An error has
occurred.","exceptionMessage":"Sequence contains no matching
element","exceptionType":"System.InvalidOperationException","stackTrace":"
at System.Linq.Enumerable.Single[TSource](IEnumerable1 source, Func2
predicate)\r\n at
PX.Api.ContractBased.SystemContracts.V2.SoapFacade.PX.Api.ContractBased.IRestGate.PutFile(EntityImpl
entityImpl, String filename, HttpContent body)\r\n at
PX.Api.ContractBased.SystemContracts.V2.RestController.PutFile(String
objectName, String ids)\r\n at lambda_method(Closure , Object ,
Object[] )\r\n at
System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass6_2.b__2(Object
instance, Object[] methodParameters)\r\n at
System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext
controllerContext, IDictionary`2 arguments, CancellationToken
cancellationToken)\r\n--- End of stack trace from previous location
where exception was thrown ---\r\n at
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task
task)\r\n at
System.Web.Http.Controllers.ApiControllerActionInvoker.d__1.MoveNext()\r\n---
End of stack trace from previous location where exception was thrown
---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task
task)\r\n at
System.Web.Http.Filters.ActionFilterAttribute.d__6.MoveNext()\r\n---
End of stack trace from previous location where exception was thrown