I'm working with ZohoBooks API for integrating with an WebApplication,
I've tried finding but failed, from where Can I get the customfield_id of items created in my zohobooks account, As i Need to create products with Custom Fields from my Application via API, I'm unable to do so.

Also invoice are to be generated as well, similar problem is happening there, Already created products with custom field all filed up, are still not showing up in invoice created via API.

Please Help, Very Urgent.