This field contains the invoice discount amount that was calculated on the line if you clicked the Functions button and then clicked Calculate Invoice Discount. If you have placed a check mark in the Prices Including VAT field, the amount displayed will include VAT.
The discount will be calculated automatically if there is a check mark in the Calc. Inv. Discount field in the Purchases & Payables Setup window and you do one of the following on the purchase document:
Click the button that has the name of the particular document type, for example, Invoice, and then click Statistics.
Click Posting, Test Report.
Click Print.
Post the document.
If you change the invoice discount amount, the program will update the contents of the Line Amount field.