Please find my implementation below:

 var testpayload = JSON.stringify({
              'formValues': [
                  {
                      '__metadata': { 'type': 'SP.ListItemFormUpdateValue' },
                      'FieldName': 'Title',
                      'FieldValue': folderName
                  },
                  {
                      '__metadata': { 'type': 'SP.Taxonomy.TaxonomyFieldValue' },
                      'Label': 'Some Label',
                      "TermGuid": "6859a10b-fdec-47e0-8632-757cc4b5e693",
                      "WssId": "-1"
                  }]
          }); $.ajax({
                  url: webUrl + "/_vti_bin/listdata.svc/" + listName,
                  type: "POST",
                  contentType: "application/json;odata=verbose",
                  data: testpayload,
                  headers: {
                      "Accept": "application/json;odata=verbose",
                      "Slug": listUrl + "/" + folderName + "|" + folderContentTypeId,
                      "X-RequestDigest": $("#_REQUESTDIGEST").val()
                  },
                  success: function (data) {
                     
                  },
                  error: error
              });

I am trying to update taxonomy field by creating testpayload but its not seems to be working.Is there any way to accomplish this?

Thanks in advance

Hi,

Here are two blogs for your reference:

Using REST to update a Managed Metadata column in SharePoint!

http://www.aerieconsulting.com/blog/using-rest-to-update-a-managed-metadata-column-in-sharepoint

Taxonomy Columns & SharePoint 2013 List REST API

http://sharepointificate.blogspot.com/2014/05/taxonomy-columns-sharepoint-2013-list.html

Best Regards