We have been using API calls to convert SO to invoice.

If SO is created directly, there is no problem.

If SO is converted from Estimate, we get message below:

code: 4102,

 message: 'Expense or projects cannot be added with item from sales order. ' }

this is zoho's "error response object" when trying to create an invoice from an estimate with an item on it

There are only regular Item product, we never use time or expense on Estimate, SO or invoice.

Please check.

Thank you.