Is it possible to add the same Tax Type with a different percentage or amount to an Invoice header?

No, it is not possible to have the same Tax Type on the header level of the Invoice.

You will need to apply the same Tax Type with a different percentage or amount to each individual Line Item. Likewise, a single Line Item cannot have multiple of the same Tax Type either.

For additional information regarding tax configuration, please see the following guide: Tax and charge configuration.

Although Suppliers can send the same Tax Type at the Header or Line Item level of the Invoice via cXML, they will run into validations during the reconciliation process.

For the out-of-the-box validation error message for the same Tax Type on a single Line Item, please see Scenario 2 in Support Note 194139: Error: "there are invalid fields in the invoice reconciliation document." when approving Invoice Reconciliation.

Invoicing