Update items

Lots of my items reach a stock level (a small amount) & stock_on_hand needs to be re-set to zero as it's not possible to top them up.

Ideally they need to be re-used again rather than making them inactive, I have tried the following but the stock_on_hand doesn't update .....

itemID = "*************";

var data = {

"stock_on_hand" : 0,

"custom_fields" : [{

"index" : indexofCustomFieldBay,

"value" : "All sold - Ready to use again"

}

]};

var url = ' https://books.zoho.com/api/v3/items/' + encodeURIComponent( itemID) + '?authtoken=' + token + '&JSONString=' + encodeURIComponent(JSON.stringify( data))

var options = {

'method' : 'put',

'contentType' : 'application/json',

'muteHttpExceptions' : true

};

var response = UrlFetchApp.fetch( url, options);

Does it have to be done a different way ?