Bug][SubscriptionBilling]: "Prices Including VAT" option does not correctly update Subscription Line amounts

src/Apps/W1/Subscription Billing/App/Billing/Codeunits/SalesDocuments.Codeunit.al

@@ -613,6 +613,7 @@ codeunit 8063 "Sales Documents"
                     else
                         SubscriptionLine.Validate("Subscription Line Start Date", CalcDate(SalesSubscriptionLine."Sub. Line Start Formula", SalesLine."Shipment Date"));
                 SubscriptionLine.CopyFromSalesServiceCommitment(SalesSubscriptionLine);
+                SubscriptionLine.EnsureCalculationBaseAmountExcludesVAT(SalesLine, SalesHeader);
                 if SalesSubscriptionLine.Discount then
                     SubscriptionLine.Validate("Calculation Base Amount", SubscriptionLine."Calculation Base Amount" * -1);
 

src/Apps/W1/Subscription Billing/App/Sales Service Commitments/Codeunits/SalesSubscriptionLineMgmt.Codeunit.al

@@ -1,5 +1,6 @@
 namespace Microsoft.SubscriptionBilling;
 
+using Microsoft.Finance.Currency;
 using Microsoft.Inventory.Item;
 using Microsoft.Sales.Archive;
 using Microsoft.Sales.Document;
@@ -387,6 +388,32 @@ codeunit 8069 "Sales Subscription Line Mgmt."
         AddSalesServiceCommitmentsForSalesLine(ToSalesLine, false);
     end;
 
+    [EventSubscriber(ObjectType::Table, Database::"Sales Header", OnValidatePricesIncludingVATOnBeforeSalesLineModify, '', false, false)]
+    local procedure RecalculateSalesSubscriptionLineAmountsOnBeforeSalesLineModify(var SalesHeader: Record "Sales Header"; var SalesLine: Record "Sales Line"; Currency: Record Currency; RecalculatePrice: Boolean)
+    var
+        SalesSubscriptionLine: Record "Sales Subscription Line";
+        VatFactor: Decimal;
+    begin
+        if not RecalculatePrice then
+            exit;
+        if SalesLine."VAT Calculation Type" = SalesLine."VAT Calculation Type"::"Full VAT" then
+            exit;
+        VatFactor := 1 + SalesLine.GetVATPct() / 100;
+        if VatFactor = 0 then
+            VatFactor := 1;
+        if not SalesHeader."Prices Including VAT" then
+            VatFactor := 1 / VatFactor;
+        SalesSubscriptionLine.FilterOnSalesLine(SalesLine);
+        SalesSubscriptionLine.SetRange(Partner, Enum::"Service Partner"::Customer);
+        if not SalesSubscriptionLine.FindSet(true) then
+            exit;
+        repeat
+            SalesSubscriptionLine.Validate("Calculation Base Amount",
+                Round(SalesSubscriptionLine."Calculation Base Amount" * VatFactor, Currency."Unit-Amount Rounding Precision"));
+            SalesSubscriptionLine.Modify(false);
+        until SalesSubscriptionLine.Next() = 0;
+    end;
+
     [IntegrationEvent(false, false)]
     local procedure OnBeforeCreateSalesSubscriptionLineFromSubscriptionPackageLine(var SalesLine: Record "Sales Line"; var SubscriptionPackageLine: Record "Subscription Package Line"; var IsHandled: Boolean)
     begin

src/Apps/W1/Subscription Billing/App/Service Commitments/Tables/SubscriptionLine.Table.al

@@ -1408,6 +1408,24 @@ table 8059 "Subscription Line"
         Rec."Currency Code" := CurrencyCode;
     end;
 
+    internal procedure EnsureCalculationBaseAmountExcludesVAT(SalesLine: Record "Sales Line"; SalesHeader: Record "Sales Header")
+    var
+        LocalCurrency: Record Currency;
+        NetBaseAmount: Decimal;
+    begin
+        if not SalesHeader."Prices Including VAT" then
+            exit;
+        if SalesLine."VAT Calculation Type" = SalesLine."VAT Calculation Type"::"Full VAT" then
+            exit;
+        if SalesLine.GetVATPct() = 0 then
+            exit;
+        LocalCurrency.Initialize(SalesHeader."Currency Code");
+        NetBaseAmount := Round(
+            Rec."Calculation Base Amount" / (1 + SalesLine.GetVATPct() / 100),
+            LocalCurrency."Unit-Amount Rounding Precision");
+        Rec.Validate("Calculation Base Amount", NetBaseAmount);
+    end;
+
     internal procedure ErrorIfBillingLineForServiceCommitmentExist()
     begin
         if BillingLineExists() then