Field help (INVDTAAMT) 

The values relate to the invoicing footer. This information can directly come from the parameters of the invoice footer or from the customer record.
SEEREFERTTO Refer to the Invoicing elements documentation for more information.
The values of the footer elements can be modified. The ex-tax and tax-incl. amounts of the document are directly impacted by these values.
Intercompany specificities
If the order has been generated from an inter-company or inter-site purchase order, and the inter-company setup stipulates that the invoicing elements come from the Purchase module, these will be initialized with the values entered in the original purchase order.