Trying to create an item group via the API
however keep getting the error "json not well formed"

My JSON is perfectly valid as Ive ran it through a lot of validators 
All I have changed is added \ before the "  as its being passing in a string

Here is the code formatted for the string 

1. JSONString='{\"group_name\": \"Test\",\"brand\": \"\",\"manufacturer\": \"\",\"unit\": \"qty\",\"description\": \"\",\"tax_id\":0 ,\"attribute_name1\": \"\",\"items\": [ { \"name\": \"Test Item\",\"rate\": 0,\"purchase_rate\":0 ,\"reorder_level\": 0,\"initial_stock\": 0,\"initial_stock_rate\": 0,\"vendor_id\": \"NULL\",\"sku\": \"\",\"upc\": 111111111111,\"ean\": 0,\"isbn\": 0,\"part_number\": 0,\"attribute_option_name1\": \"\"}],\"attributes\": [{\"id\": \"NULL\",\"name\": \"Test small\",\"options\": [{\"id\": \"NULL\",\"name\": \"Test Small\"}]}]}}'"
   

Here is the code without the \ before the "

1. {"group_name": "Test","brand": "","manufacturer": "","unit": "qty","description": "","tax_id":0 ,"attribute_name1": "","items": [ { "name": "Test Item","rate": 0,"purchase_rate":0 ,"reorder_level": 0,"initial_stock": 0,"initial_stock_rate": 0,"vendor_id": "NULL","sku": "","upc": 111111111111,"ean": 0,"isbn": 0,"part_number": 0,"attribute_option_name1": ""}],"attributes": [{"id": "NULL","name": "Test small","options": [{"id": "NULL","name": "Test Small"}]}]}}
   

Ideally I wanted to add as little info as possible .. just the group name , unit  and 1 item ( just the required fields )
instead of having to include all the information like i have above

I really cant see what the issue is

Here is my complete cURL code ( without the auth token obviously )

1. header('Content-Type: application/json');
   $ch = curl_init();
   curl_setopt($ch, CURLOPT_URL, "https://inventory.zoho.com/api/v1/itemgroups?authtoken=XXXXXXXXd&organization_id=674140431");
   curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
   curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
   curl_setopt($ch, CURLOPT_POSTFIELDS, "JSONString='{\"group_name\": \"Test\",\"brand\": \"\",\"manufacturer\": \"\",\"unit\": \"qty\",\"description\": \"\",\"tax_id\":0 ,\"attribute_name1\": \"\",\"items\": [ { \"name\": \"Test Item\",\"rate\": 0,\"purchase_rate\":0 ,\"reorder_level\": 0,\"initial_stock\": 0,\"initial_stock_rate\": 0,\"vendor_id\": \"NULL\",\"sku\": \"\",\"upc\": 111111111111,\"ean\": 0,\"isbn\": 0,\"part_number\": 0,\"attribute_option_name1\": \"\"}],\"attributes\": [{\"id\": \"NULL\",\"name\": \"Test small\",\"options\": [{\"id\": \"NULL\",\"name\": \"Test Small\"}]}]}}'");
   curl_setopt($ch, CURLOPT_POST, true);
   $result = curl_exec($ch);
   if (curl_errno($ch)) {
       echo 'Error:' . curl_error($ch);
   }
   curl_close ($ch);
   echo $result;