so I have this code that removes and adds new line in Invoice via aftersubmit user event script.

It looks like this:

record.removeLineItem(sublist, linenum);

record.insertLineItem(sublist, linenum, false);

record.setLineItemValue(sublist, "item", linenum, item);

record.setLineItemValue(sublist, "description", linenum, description);

record.setLineItemValue(sublist, "rate", linenum, rate);

....

nlapiSubmitRecord(record, true);

If like this, my script will run successfully but the Amount and Tax Fields, and Gross Amount field is not automatically populated.

if I add lines to set the amount, gross amount and tax code like this:

record.setLineItemValue(sublist, "amount", linenum, newAmount);

record.setLineItemValue(sublist, "taxcode", linenum, taxcode);