Whenever i try to do an Addinventoryrequest it comes up 400 BadRequest,

i've managed to make other calls such as GetPostalServices() , GetPackageGroup()

i've posted the reqeuest below. if anyone can help me!

POST //api/Inventory/AddInventoryItem HTTP/1.1
> Host: eu-ext.linnworks.net
> User-Agent: insomnia/6.0.2
> Authorization: ********-****-****-****-************             

> Accept: */*
> Content-Length: 810
| inventoryItem=
| {
|     "Quantity":1,
|     "InOrder":0,
|     "Due":0,
|     "MinimumLevel":-1,
|     "Available":0,
|     "CreationDate":null,
|     "IsCompositeParent":null,
|     "ItemNumber":"77367369",
|     "BarcodeNumber":"0077367369001",
|     "MetaData":"Test Product",
|     "IsBatchedStockType":true,
|     "PurchasePrice":5.0,
|     "TaxRate":-1.0,
|     "PostalServiceId":"f6ee9abf-2cc0-47e4-bcbe-93c90cdeb288",
|     "PostalServiecName":"Standard",
|     "CategoryId":"e4779fa0-906b-40d6-8ea9-2076789a3e1f",
|     "CategoryName":"Brake Pads","PackageGroupId":"71933444-7591-4b4c-bb25-cb319180a2d4",
|     "PackageGroupName":"Packet - Jiffy Bag",
|     "Height":0.0,
|     "Width":0.0,
|     "Depth":0.0,
|     "Weight":0.0,
|     "InventoryTrackingType":1,
|     "BatchNumberscanRequired":false,
|     "SerielNumberScanRequired":false,
|     "StockItemId":"a699ed14-6339-4406-a0d9-488d0c824a7d"
| }
* upload completely sent off: 810 out of 810 bytes
< HTTP/1.1 400 Bad Request
< Date: Mon, 24 Sep 2018 11:57:53 GMT
< Content-Type: application/json; charset=utf-8
< Content-Length: 40
< Connection: keep-alive
< Cache-Control: no-cache
< Pragma: no-cache
< Expires: -1
< Server: Microsoft-IIS/8.5
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Headers: *
< Access-Control-Allow-Credentials: false
< X-AspNet-Version: 4.0.30319
< X-Powered-By: ASP.NET
< Access-Control-Allow-Headers: Authorization, Origin, X-Requested-With, Content-Type, Accept, Accept-Language
< Access-Control-Allow-Methods: GET, POST, OPTIONS
< Access-Control-Allow-Credentials: true

* Received 40 B chunk
* Connection #10 to host eu-ext.linnworks.net left intact