I found the problem, although, it seems like a Shopify bug. We had changed the name of the website store name from example "the-store-name" to "the-store" a while back. Keeping this in mind, I changed the URL in my code from: "https://the-store-name....

the simple jsonString = {    "product": {        "title": "Some Suit",        "body_html": "You should wear this",        "vendor": "Top Vendor",        "product_type": "Womens Suit",        "status": "draft"    }} //The code is using System.Net.WebC...