Problem with creating item to Zoho inventory with POST request

Problem with creating item to Zoho inventory with POST request

Hello, I am trying to add item to Zoho inventory using nodejs POST request. But I keep getting the following error: 
  1. {"code":4,"message":"Invalid value passed for JSONString"}
Here is the code for the POST request:

  1. let form = {
  2.         unit: "qty",
  3.         item_type: "inventory",
  4.         product_type: "goods",
  5.         is_taxable: true,
  6.         description: "description",
  7.         attribute_name1: "Small",
  8.         name: "Bags-small",
  9.         rate: 6,
  10.         purchase_rate: 6,
  11.         reorder_level: 5,
  12.         initial_stock: 50,
  13.         initial_stock_rate: 500,
  14.         sku: "SK123",
  15.         upc: 111111111111,
  16.         ean: 111111111112,
  17.         isbn: 111111111113,
  18.         part_number: 111111111114,
  19.         attribute_option_name1: "Small",
  20.         purchase_description: "Purchase description"
  21.     };

  23.     let formData = JSON.stringify(form);
  24.     console.log(formData);

  26.     request({
  27.         headers: {
  28.             'Authorization': 'Zoho-authtoken d9XXXXXXXXXXXXXXXXXd0f46',
  29.             'organization_id': '667953382'
  30.         },
  31.         uri: 'https://inventory.zoho.com/api/v1/items?authtoken=d9XXXXXXXXXXXXXXXX0f46&organization_id=6XXXXXXX2',
  32.         body: formData,
  33.         method: 'POST'
  34.     }, function (err, res, body) {
  35.         console.log(body); // get error message here
  36.     });
Although the JSON is valid, I get the same error when trying with Postman. Can you please let me know what I am missing here? Thank you