https://userapps.support.sap.com/sap/support/knowledge/en/3550144
3550144 - Field BELNR is empty within database table VTBFHAPO | SAP Knowledge Base Article
When displaying the entries for database table VTBFHAPO the document number (BELNR) for all Posted Treasury Financial Transactions is empty.
https://userapps.support.sap.com/sap/support/knowledge/en/2890145
2890145 - BELNR field doesn't appear in calculation view - S/4HANA 1610 | SAP Knowledge Base Article
When creating a foundation view, the field BELNR is not available