fix: updating gathering invoices with split lines

openmeter/billing/service/invoice.go

@@ -901,6 +901,22 @@ func (s *Service) UpdateInvoice(ctx context.Context, input billing.UpdateInvoice
 				return billing.Invoice{}, fmt.Errorf("fetching invoice: %w", err)
 			}
 
+			// We have requested the invoice to include the split lines, and GetInvoiceByID will also expand
+			// the sub-lines. However given split lines are cross invoice, those should not be edited via single
+			// invoice update calls, so we strip the child line information from the invoice. This signals the adapter
+			// that we are not trying to edit the child lines, thus it will not throw an error for the operation.
+
+			invoice.Lines = billing.NewLineChildren(lo.Map(invoice.Lines.OrEmpty(), func(line *billing.Line, _ int) *billing.Line {
+				if line.Status != billing.InvoiceLineStatusSplit {
+					return line
+				}
+
+				// This makes the line children not present in the invoice
+				line.Children = billing.LineChildren{}
+
+				return line
+			}))
+
 			if err := input.EditFn(&invoice); err != nil {
 				return billing.Invoice{}, fmt.Errorf("editing invoice: %w", err)
 			}