If your organization is based out of the U.S.A. or Canada and if you have enabled the integration with Avalara, then the field Shipping Charges will not be available while creating invoices, estimates etc. This is because shipping is also taxable in these countries.
You can include shipping charges while creating invoices by adding it as a line item. Create a new item called “Shipping”, enter the Rate and specify the tax code as FR(Freight).
Henceforth, whenever you create an invoice for a customer, after adding all the products as line items, include the item “Shipping” as well.