Salesforce Billing Invoice Line generates with 0 for blng__Quantity__c

First, confirm if Invoice Plans are defined and no Invoice Lines manually define quantity. To determine whether Sub Invoice Lines exist for a given Invoice Line, review the Invoice Line Type field (blng__InvoiceLineState__c). You can also examine the Sub Invoice Lines related list to verify the associated records and confirm the total quantity.

Invoice Line Type values:

• Merged – Indicates that Sub Invoice Lines are associated with the Invoice Line.
• Regular – Indicates that no Sub Invoice Lines exist for the Invoice Line.