Time Zone is underfined when creating WO by API

when we tried to create WO by API, we got error message on 'Time Zone is undefined' in sandbox. here to attach our code.

client ID: ceapiclient.1.5915.e03a.0007

{
"Command" : {
"WorkOrder" : {
"Items" : [
{
"Asset" : {
"Id" : 99168
},
"Task" : {
"Id" : 23429
}
}
],
"Contactid":2,
"TypeCategory" : 4,

     "SubType" : {
        "Id" : 259
     },
     "Customer" : {
        "Id" : 99162
     }
  },
  "ComputeSchedule" : true

},
"RequestId" : "0242422.3341"
}_