[Bug]: Inbound German e-documents are accepted without validating mandatory EN 16931 fields

Describe the issue

When an inbound German electronic invoice is imported into Business Central, mandatory data elements required by EN 16931 are not consistently validated.

If mandatory information is missing or invalid, the document can still be imported and stored. Missing values may be mapped to empty fields without a validation error, warning, or clear indication that the document is not compliant.

This affects inbound ZUGFeRD and XRechnung documents.

Expected behavior

Business Central should validate inbound German electronic invoices against the applicable EN 16931 requirements and the relevant ZUGFeRD/XRechnung business rules.

If a mandatory element is missing or invalid, Business Central should:

• reject the document or clearly set it to an invalid/error status;
• display a meaningful validation message;
• identify the affected EN 16931 business term or field;
• prevent the document from being treated as a valid inbound e-document.

Steps to reproduce

1. Create or obtain a German ZUGFeRD or XRechnung invoice.
2. Remove or invalidate a mandatory EN 16931 element, for example:
   • BT-1: Invoice number
   • BT-2: Invoice issue date
   • BT-5: Invoice currency code
   • BT-44: Buyer name
   • BG-23: VAT breakdown
   • BT-112 / BT-115: Invoice totals
3. Import the document as an inbound e-document in Business Central.
4. Process or open the imported e-document.
5. Observe that the document is accepted or stored without an appropriate validation error.

Additional context

This issue is related to the previously reported issue:
https://github.com/microsoft/ALAppExtensions/issues/30263

The issue concerns inbound validation. Existing validation logic appears to be used primarily in the outbound/send scenario and is not consistently applied when receiving German e-documents.

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