How to group subscription lines and freight line interface to create a single AR invoice

Summary:

Requirement is to insert a new freight line for SMC order at AR interface lines (Manage Autoinvoice lines) and import into AR.

Steps:

1. Create a subscription order and make interface to AR
2. Go to AR > Billing > Task List > Manage Autoinvoice lines
3. Download the file and search with order number
4. Insert a new record to enter line type as freight and other details using soup UI
5. Created grouping rule based on INTERFACE_LINE_ATTRIBUTE1(Subscription Number) - Both subscription lines and freight line having same subscription number
6. Click on submit

Here the issue is We have able to insert a freight line at AR_INTERFACE for the same subscription lines, Add we have, But in receivables system created 2 different invoices, 1 for subscriptions lines and 2nd for freight amount. Could you please provide the solution how to add the freight amount onto subscription lines before imported.