HTTP POST to create a new Work Order in Microsoft Dynamics 365 - Field Service (Empty body)

import requests

url = "https://{{my-env_name}}.{{my_region}}.dynamics.com/api/data/v9.0/msdyn_workorders"

payload = "{\n   \n}"
headers = {
  'Accept': 'application/json',
  'OData-MaxVersion': '4.0',
  'OData-Version': '4.0',
  'If-None-Match': 'null',
  'Authorization': 'Bearer eyXXX',
  'Content-Type': 'application/json',
}

response = requests.request("POST", url, headers=headers, data = payload)

print(response.text.encode('utf8'))

Error received when the Body of the POST is empty

{
    "error": {
        "code": "0x80040265",

        "message": "The Service Account is required.",

        "innererror": {
            "message": "The Service Account is required.",

            "type": "System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=9.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]",

            "stacktrace": "   at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.CreateInternal(Entity entity, InvocationContext invocationContext, CallerOriginToken callerOriginToken, WebServiceType serviceType, Boolean checkAdminMode, Dictionary`2 optionalParameters)\r\n

   at Microsoft.Crm.Extensibility.OData.CrmODataExecutionContext.CreateOrganizationResponse(Entity entity)\r\n

   at Microsoft.Crm.Extensibility.OData.CrmODataServiceDataProvider.CreateEdmEntity(CrmODataExecutionContext context, String edmEntityName, EdmEntityObject entityObject, Boolean isUpsert)\r\n

   at Microsoft.Crm.Extensibility.OData.EntityController.PostEntitySetImplementation(String& entitySetName, EdmEntityObject entityObject)\r\n

   at Microsoft.Crm.Extensibility.OData.CrmODataUtilities.<>c__DisplayClass10_0`2.<InvokeActionAndLogMetric>b__0()\r\n

   at Microsoft.PowerApps.CoreFramework.ActivityLoggerExtensions.Execute[TResult](ILogger logger, EventId eventId, ActivityType activityType, Func`1 func, IEnumerable`1 additionalCustomProperties)\r\n

   at Microsoft.Xrm.Telemetry.XrmTelemetryExtensions.Execute[TResult](ILogger logger, XrmTelemetryActivityType activityType, Func`1 func)\r\n

   at lambda_method(Closure , Object , Object[] )\r\n

   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(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.<InvokeActionAsyncCore>d__0.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.Controllers.ActionFilterResult.<ExecuteAsync>d__2.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.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"
        }
    }
}

I add the Service Account into the body of the POST

Look at the model of a Work Order : https://docs.microsoft.com/en-us/dynamics365/customer-engagement/web-api/msdyn_workorder?view=dynamics-ce-odata-9

{
  "msdyn_serviceaccount": "{{an existing account id}}"
}

Error received when the Body of the POST contains the msdyn_serviceaccount field

{
    "error": {

        "code": "0x0",


        "message": "An error occurred while validating input parameters: Microsoft.OData.ODataException: A 'PrimitiveValue' node with non-null value was found when trying to read the value of the property 'msdyn_serviceaccount'; however, a 'StartArray' node, a 'StartObject' node, or a 'PrimitiveValue' node with null value was expected.\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightPropertyAndValueDeserializer.ValidateExpandedNestedResourceInfoPropertyValue(IJsonReader jsonReader, Nullable`1 isCollection, String propertyName)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.ReadPropertyWithValue(IODataJsonLightReaderResourceState resourceState, String propertyName, Boolean isDeltaResourceSet)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.<>c__DisplayClass9_0.<ReadResourceContent>b__0(PropertyParsingResult propertyParsingResult, String propertyName)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightDeserializer.ProcessProperty(PropertyAndAnnotationCollector propertyAndAnnotationCollector, Func`2 readPropertyAnnotationValue, Action`2 handleProperty)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.ReadResourceContent(IODataJsonLightReaderResourceState resourceState)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightReader.StartReadingResource()\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightReader.ReadResourceSetItemStart(PropertyAndAnnotationCollector propertyAndAnnotationCollector, SelectedPropertiesNode selectedProperties)\r\n   at 

Microsoft.OData.JsonLight.ODataJsonLightReader.ReadAtStartImplementationSynchronously(PropertyAndAnnotationCollector propertyAndAnnotationCollector)\r\n 

  at Microsoft.OData.ODataReaderCore.ReadImplementation()\r\n

   at Microsoft.OData.ODataReaderCore.InterceptException[T](Func`1 action)\r\n

   at System.Web.OData.Formatter.Deserialization.ODataReaderExtensions.ReadResourceOrResourceSet(ODataReader reader)\r\n

   at System.Web.OData.Formatter.Deserialization.ODataResourceDeserializer.Read(ODataMessageReader messageReader, Type type, ODataDeserializerContext readContext)\r\n

   at System.Web.OData.Formatter.ODataMediaTypeFormatter.ReadFromStream(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)",
        "innererror": {

            "message": "An error occurred while validating input parameters: Microsoft.OData.ODataException: A 'PrimitiveValue' node with non-null value was found when trying to read the value of the property 'msdyn_serviceaccount'; however, a 'StartArray' node, a 'StartObject' node, or a 'PrimitiveValue' node with null value was expected.\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightPropertyAndValueDeserializer.ValidateExpandedNestedResourceInfoPropertyValue(IJsonReader jsonReader, Nullable`1 isCollection, String propertyName)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.ReadPropertyWithValue(IODataJsonLightReaderResourceState resourceState, String propertyName, Boolean isDeltaResourceSet)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.<>c__DisplayClass9_0.<ReadResourceContent>b__0(PropertyParsingResult propertyParsingResult, String propertyName)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightDeserializer.ProcessProperty(PropertyAndAnnotationCollector propertyAndAnnotationCollector, Func`2 readPropertyAnnotationValue, Action`2 handleProperty)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightResourceDeserializer.ReadResourceContent(IODataJsonLightReaderResourceState resourceState)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightReader.StartReadingResource()\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightReader.ReadResourceSetItemStart(PropertyAndAnnotationCollector propertyAndAnnotationCollector, SelectedPropertiesNode selectedProperties)\r\n

   at Microsoft.OData.JsonLight.ODataJsonLightReader.ReadAtStartImplementationSynchronously(PropertyAndAnnotationCollector propertyAndAnnotationCollector)\r\n

   at Microsoft.OData.ODataReaderCore.ReadImplementation()\r\n

   at Microsoft.OData.ODataReaderCore.InterceptException[T](Func`1 action)\r\n

   at System.Web.OData.Formatter.Deserialization.ODataReaderExtensions.ReadResourceOrResourceSet(ODataReader reader)\r\n

   at System.Web.OData.Formatter.Deserialization.ODataResourceDeserializer.Read(ODataMessageReader messageReader, Type type, ODataDeserializerContext readContext)\r\n

   at System.Web.OData.Formatter.ODataMediaTypeFormatter.ReadFromStream(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)",
            "type": "Microsoft.Crm.CrmHttpException",
            "stacktrace": "   at Microsoft.Crm.Extensibility.OData.CrmODataUtilities.ValidateInputParameters(ModelStateDictionary controllerModelState)\r\n

   at Microsoft.Crm.Extensibility.OData.EntityController.PostEntitySetImplementation(String& entitySetName, EdmEntityObject entityObject)\r\n

   at Microsoft.Crm.Extensibility.OData.CrmODataUtilities.<>c__DisplayClass10_0`2.<InvokeActionAndLogMetric>b__0()\r\n

   at Microsoft.PowerApps.CoreFramework.ActivityLoggerExtensions.Execute[TResult](ILogger logger, EventId eventId, ActivityType activityType, Func`1 func, IEnumerable`1 additionalCustomProperties)\r\n

   at Microsoft.Xrm.Telemetry.XrmTelemetryExtensions.Execute[TResult](ILogger logger, XrmTelemetryActivityType activityType, Func`1 func)\r\n

   at lambda_method(Closure , Object , Object[] )\r\n

   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(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.<InvokeActionAsyncCore>d__0.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.Controllers.ActionFilterResult.<ExecuteAsync>d__2.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.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"
        }
    }
}

QUESTION: What is the expected JSON body by the Web API of Microsoft Dynamics 365 Field Service?

You should use this, to put in a lookup (aka Entity reference, navigation property):

{
  "msdyn_serviceaccount@odata.bind": "/accounts(guid)"
}

The basic payload with required fields to create work order is below:

{
   "msdyn_serviceaccount@odata.bind": "/accounts(account_entity_guid_you_want_to_bind)",    
   "msdyn_pricelist@odata.bind": "/pricelevels(pricelevel_entity_guid_you_want_to_bind)",    
   "msdyn_systemstatus": "690970000",    
}

Reference