Create a tax category

{
  "data": {
    "attributes": {
      "code": "31000",
      "sku_code": "TSHIRTMM000000FFFFFFXLXX",
      "reference": "ANY-EXTERNAL-REFEFERNCE",
      "reference_origin": "ANY-EXTERNAL-REFEFERNCE-ORIGIN",
      "metadata": {
        "foo": "bar"
      }
    },
    "relationships": {
      "sku": {
        "data": {
          "id": "XAyRWNUzyN"
        }
      },
      "tax_calculator": {
        "data": {
          "id": "XAyRWNUzyN",
          "attributes": {
            "name": "Personal tax calculator",
            "type": "avalara_accounts",
            "created_at": "2018-01-01T12:00:00.000Z",
            "updated_at": "2018-01-01T12:00:00.000Z",
            "reference": "ANY-EXTERNAL-REFEFERNCE",
            "reference_origin": "ANY-EXTERNAL-REFEFERNCE-ORIGIN",
            "metadata": {
              "foo": "bar"
            },
            "username": "user@mydomain.com",
            "company_code": "MYCOMPANY",
            "commit_invoice": true,
            "ddp": true,
            "pass_tax_exemption_code": true
          },
          "relationships": {
            "markets": {
              "data": {
                "id": "XAyRWNUzyN"
              }
            },
            "attachments": {
              "data": {
                "id": "XAyRWNUzyN"
              }
            },
            "events": {
              "data": {
                "id": "XAyRWNUzyN"
              }
            },
            "event_stores": {
              "data": {
                "id": "XAyRWNUzyN"
              }
            },
            "tax_categories": {
              "data": {
                "id": "XAyRWNUzyN"
              }
            }
          }
        }
      }
    }
  }
}