I have customers with different billing rates for the same non-inventory item which is a service. I’ve added the the billing rate in the customer information as a custom field. I’ve also added a custom sales invoice — line item. Is there a way to populate either the new sales invoice line item or the unit price with the customer billing rate on the sales invoice?
No. Custom fields are unique to the form for which they were designed. So a custom field for a customer cannot appear on a sales invoice line item. And contents of custom fields cannot be substituted for unit price.
However, if a custom field is defined for a customer and checked show on printed documents, it will appear below the balance due, along with custom fields defined for that form. For example, in the example below, Notes is a custom field defined for sales invoices. Telephone and Point of Contact are custom fields defined for the customer selected for this particular sales invoice: