Using SAP B1 SDK (v9.2) to update Tax Amount (AP Invoice)

[former_member201155]

Environment:
SAP B1 9.92

VB.NET

Steps to duplicate:

In SAP B1's AP invoice UI,
I set:
Line Quantity is 1, Price is $10.00, VAT code is 'VAT10%', Tax Amount is $2.00
NB: VAT10% rate is 10%
After saved:
AP Invoice total is $12.00, Discount is $0.00
AP Invoice line values remained same as entered.

In VB.NET (SAP B1 SDK API)'s AP invoice creation,
I set:
Header.DocTotal = 12.00
Line.Quantity = 1, Line.Price = 10, Line.PriceAfVAT = 12, Line.VatGroup = 'VAT10%', Line.TaxTotal = $2.00
NB: VAT10% rate is 10%
After saved:
AP Invoice total is $12.00, Discount is -$1.00 (instead of $0.00)
Some of the fields value in AP Invoice line is different from what I set earlier:
Gross Total (LC) is $11.00 (instead of $12.00), Tax Amount (LC) is $1.00 (instead of $2.00)

Issue:

We are happy that we are able to override the AP invoice line tax amount via SAP B1 UI instead of letting it auto-calculated based on Vat %.

However, how do I override the AP invoice line tax amount via SDK API?

Thanks.