We are trying to generate invoices using Zoho books APIs from our application. 

When creating an invoice manually in Books portal, we can enter items which are not present in inventory, but when using the API we could not do the same.

Also, we have a service as a line item, which has no fixed rate, and changes from customer to customer.

1. Is there a way to pass item rate when creating an invoice through API ?

2. Can we add items to invoices which haven't been added to inventory when using API ?