Getting invalid Windows Store receipts

I'm trying to implement IAP in the Windows store, but the receipts Unity is returning to me won't validate. Here's an example receipt I'm receiving:

 <?xml version=\"1.0\"?><Receipt Version=\"2.0\" CertificateId=\"A656B9B1B3AA509EEA30222E6D5E7DBDA9822DCD\" xmlns=\"http://schemas.microsoft.com/windows/2012/store/receipt\"><ProductReceipt PurchasePrice=\"USD0\" PurchaseDate=\"2018-01-26T18:55:45.243Z\" Id=\"c683f446-67f0-4b5c-8308-fe650acc8f87\" AppId=\"SonyPicturesTelevision.PlaytheShow_xhagv60wx4y2m\" ProductId=\"Pack_StarterPack_01\" ProductType=\"Durable\" PublisherUserId=\"JAHTYOzCxMy0f7ZyC+0w1LRsK2TdyVscTo8EuzpSODQ=\" MicrosoftProductId=\"7a31d10d-4d6a-4f3e-9f40-0136eb10002d\" MicrosoftAppId=\"7a31d10d-4d6a-4f3e-9f40-0136eb10002d\" ExpirationDate=\"9999-12-31T23:59:59.999Z\" OfferId=\"\" /><Signature xmlns=\"http://www.w3.org/2000/09/xmldsig#\"><SignedInfo><CanonicalizationMethod Algorithm=\"http://www.w3.org/TR/2001/REC-xml-c14n-20010315\" /><SignatureMethod Algorithm=\"http://www.w3.org/2001/04/xmldsig-more#rsa-sha256\" /><Reference URI=\"\"><Transforms><Transform Algorithm=\"http://www.w3.org/2000/09/xmldsig#enveloped-signature\" /></Transforms><DigestMethod Algorithm=\"http://www.w3.org/2001/04/xmlenc#sha256\" /><DigestValue>neMDm4gb4mwS55v8JCi6Qbm6UcuRjcuurxytvMXlENc=</DigestValue></Reference></SignedInfo><SignatureValue>vzdoTgSoxwoIQcBjo8Pav1aw8OcabRJMIEttN3U3l9nxQT5GUpmRVJESqcWjQoVkx7wpnidPZw20JC5mO0a/FEoQAvAhgL2W8Abq14OQaDpmMhgan5yPdjQhZj296BCqAANpcGqdTCXWedku2dSeWEem+e4JY+3L7KZj/ZmM3BgMlacIB01dm7Y/+CQK40+OwUTIWHvqFq+j0XjEw9Z0K3kl53YWob7NievCgo0K9gIZy6RqtKFcWiWOqH3eJD/BAKG1mVjy7XNDz/aipfzJrbFZ7NFJqSqIwROVUfdMzbG2Jv/D6bB92FEf9I4fp+fo98ju5C4yGi+zjp3pFoOiKQ==</SignatureValue></Signature></Receipt>

Notably, the Receipt element is missing the required ReceiptDate and ReceiptDeviceID fields.

The way I'm getting the receipt is as follow:

 public PurchaseProcessingResult ProcessPurchase(PurchaseEventArgs args)
     {
         //Parse Unity receipt JSON for actual Windows Store receipt
         var receipt = JsonConvert.DeserializeObject<UnityReceipt>(args.purchasedProduct.receipt);
         string windowsReceipt = receipt.payload;
         playfab.ValidateReceipt(windowsReceipt, args.purchasedProduct.metadata.localizedPrice, args.purchasedProduct.metadata.isoCurrencyCode, receipt.store, args.purchasedProduct.definition.id);
 
         return PurchaseProcessingResult.Complete;
     }

Does anyone know what could be wrong here?

Thank you.