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

[miljance]

Describe the issue

When working with Microsoft Subscription Billing, the handling of the "Prices Including VAT" option in Sales Orders does not correctly update the values in Sales Subscription Lines. This leads to inconsistent and incorrect reporting of amounts, particularly in downstream analytics such as Power BI reports.

The core problem is:

• The Calculation Base Amount and Price fields in Subscription Lines can contain mixed VAT-inclusive or VAT-exclusive values depending on how the Sales Order was created.
• Changing the "Prices Including VAT" checkbox on the Sales Header does not update the values in Sales Subscription Lines.
• For the same customer, documents may exist with or without VAT, creating further inconsistencies.
• The Power BI Subscription Billing report expects values without VAT, leading to inaccurate statistics when VAT-inclusive values are stored.

Expected behavior

1. Subscription Lines should always contain VAT-exclusive values (net amounts).
2. Contract Lines should also always contain VAT-exclusive values.
3. Changing the "Prices Including VAT" checkbox on the Sales Header should recalculate and update the values in Sales Subscription Lines accordingly.

Steps to reproduce

1. Create demo data for Microsoft Subscription Billing.
2. Create a customer with the option "Prices Including VAT" = true.
3. Create a new Sales Order for this customer.
4. Add a sales line for a subscription item (e.g., SB1100 Digital Newspaper, Quantity = 1).
   • ❌ The fields Calculation Base Amount and Price in Sales Subscription Lines contain VAT-inclusive values.
5. Change the Sales Order option "Prices Including VAT" to false.
   • ❌ Calculation Base Amount and Price in Subscription Lines still show VAT-inclusive values.
6. Switch the Sales Order option back to true and post the order.
   • ❌ The posted Subscription Lines continue to contain VAT-inclusive values.

Additional context

All amounts in Subscription Lines and Contract Lines should be net amounts (without VAT). The current behavior results in incorrect data being stored, which propagates into reporting tools such as the Power BI Subscription Billing report.

I will provide a fix for a bug

• I will provide a fix for a bug