Fix #7399: Strip VAT from Subscription Line base amount when Prices Including VAT is enabled

[jeffreybulanadi]

Summary

Fixes #7399

When Prices Including VAT is enabled on a Sales Header, the Calculation Base Amount on Sales Subscription Lines was incorrectly storing the VAT-inclusive unit price instead of the net price. Additionally, toggling the flag on an existing document did not trigger recalculation of already-created subscription lines.

Root Cause

Bug 1 - Wrong amount at line creation:
CalculateCalculationBaseAmountCustomer copied SalesLine."Unit Price" directly into Calculation Base Amount without checking SalesHeader."Prices Including VAT". When the flag is true, SalesLine."Unit Price" is VAT-inclusive, so subscription lines stored a gross price.

Bug 2 - No recalculation on PIV toggle:
UpdateSalesServiceCommitmentCalculationBaseAmount in SalesLine.TableExt.al exits early when Unit Price has not changed. Toggling Prices Including VAT on the Sales Header does not change the numeric value of Unit Price (same number, different interpretation), so the early-exit fires and subscription lines are never updated.

Changes

• CalculateCalculationBaseAmountCustomer: call GetSalesHeader to read the Prices Including VAT flag and strip VAT from the calculated base amount using the formula Amount / (1 + VAT% / 100) when the flag is true.
• GetSalesHeader: add an override path using SalesHeaderOverride so that an in-memory Sales Header record can be injected. This is required because OnAfterValidateEvent fires before the record is committed to the database, so a direct Get would return the old value.
• SetSalesHeader: new procedure following the same pattern as SetSalesLine, allowing callers to inject an in-memory Sales Header for accurate Prices Including VAT reads.
• SalesSubscriptionLineMgmt: add event subscriber on Sales Header OnAfterValidateEvent for Prices Including VAT to recalculate all Sales Subscription Lines when the flag is toggled.

How to Test

1. Create a VAT posting setup with a non-zero VAT% (e.g. 21%).
2. Create an item with a Subscription Package.
3. Create a Sales Order with Prices Including VAT = true.
4. Add a sales line with the subscription item at unit price 121.
5. Verify that the Sales Subscription Line Calculation Base Amount = 100 (net price, VAT stripped).
6. Toggle Prices Including VAT to false on the Sales Order.
7. Verify that the Sales Subscription Line Calculation Base Amount updates to 121 (gross price, no stripping).
8. Toggle back to true and verify the amount returns to 100.

[pri-kise]

Will you add some automatic tests?

[pri-kise]

Not the Currency TestFields are missing in this case?
Is this on purpose?

[pri-kise]

Microsoft introduced the procedure GetVATPct in the SalesLine some versions ago.
https://github.com/microsoft/BusinessCentralApps/blob/020503c3e3530c3fe56890c4a409afdf22037b45/App/Layers/W1/BaseApp/Sales/Document/SalesLine.Table.al#L11028-L11036
I'm not sure why the did this, but this used anywhere in the Salesline table.
Therfore I would suggest to use it, too.

[Copilot]

Pull request overview

Fixes Subscription Billing’s Sales Subscription Line “Calculation Base Amount” so it reflects the correct net unit price when Prices Including VAT is enabled, and ensures existing subscription lines are recalculated when the header flag is toggled.

Changes:

• Strip VAT from calculated base amount when Sales Header."Prices Including VAT" is true.
• Add an in-memory Sales Header override path (SetSalesHeader + SalesHeaderOverride) so calculations during validation read the updated flag value.
• Add a Sales Header OnAfterValidateEvent subscriber for Prices Including VAT to recalculate existing Sales Subscription Lines.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Apps/W1/Subscription Billing/App/Sales Service Commitments/Tables/SalesSubscriptionLine.Table.al	Reads Prices Including VAT via GetSalesHeader, strips VAT from base amount, and supports injected Sales Header override via SetSalesHeader.
src/Apps/W1/Subscription Billing/App/Sales Service Commitments/Codeunits/SalesSubscriptionLineMgmt.Codeunit.al	Recalculates Sales Subscription Lines when Prices Including VAT is toggled on Sales Header.

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[Copilot]

New behavior (stripping VAT from calculation base amount when Prices Incl. VAT is enabled, and recalculation when toggling the flag) is not covered by automated tests. There is an existing Sales Service Commitment Test suite; adding a test that (1) creates a sales order with non-zero VAT%, Prices Incl. VAT=true and verifies the created Sales Subscription Line base amount is net, and (2) toggles Prices Incl. VAT and verifies base amount updates, would prevent regressions.

[Copilot]

Prices Including VAT handling here uses SalesLine.GetVATPct() and a generic gross-to-net division. In this app, VAT% is explicitly treated as 0 for Reverse Charge VAT/Sales Tax (see existing VAT buffer logic), and Sales Tax requires SalesTaxCalculate.ReverseCalculateTax(...) to derive the net price. As-is, Sales Tax documents (and potentially reverse charge depending on what GetVATPct() returns) can keep a tax-inclusive base amount or be reverse-calculated incorrectly. Consider branching on SalesLine."VAT Calculation Type": for Sales Tax use ReverseCalculateTax with the sales header’s tax fields; for Reverse Charge VAT treat the effective % as 0 (no stripping).

[Copilot]

This subscriber recalculates subscription lines for every sales line on the document and recalculates vendor-partner subscription lines as well. Since Prices Including VAT only affects customer pricing, consider filtering to Partner::Customer (and possibly Process/other relevant filters) before FindSet() to avoid unnecessary queries/modifications, and/or iterating subscription lines via FilterOnDocument(Rec."Document Type", Rec."No.") to reduce work on documents with many non-subscription sales lines.

[jeffreybulanadi]

Addressing review comments (commits 9be59b7 + 2fc0d32):

Re: Currency TestFields missing in override path
Fixed - SalesHeaderOverride branch now has full parity with the database-read path:

else begin
    SalesHeaderOverride.TestField("Currency Factor");
    Currency.Get(SalesHeaderOverride."Currency Code");
    Currency.TestField("Unit-Amount Rounding Precision");
    Currency.TestField("Amount Rounding Precision");
end;

Re: Use GetVATPct() instead of direct field access
Fixed - SalesLine.GetVATPct() is now used to follow the extensibility pattern (raises OnAfterGetVATPct).

Automated tests
Three tests added to SalesServiceCommitmentTest (codeunit 139915, SalesServiceCommitmentTest.Codeunit.al) covering both bugs:

• BaseAmountIsNetPriceWhenPricesIncludingVATEnabled - creates a Sales Order with Prices Including VAT = true, asserts Calculation Base Amount = Round(UnitPrice / (1 + VAT% / 100), Unit-Amount Rounding Precision).
• BaseAmountEqualsUnitPriceWhenPricesExcludingVAT - regression guard for the standard PIV = false path (base amount must equal unit price, no stripping).
• TogglingPricesIncludingVATRecalculatesBaseAmount - starts with PIV = false, toggles to true, verifies base amount recalculates to net price; toggles back to false, verifies it reverts to unit price.