How to create unbilled invoice in Receivables?

Summary:

How to create an unbilled transaction in receivables with accounting and without Revenue scheduling rules?
Once revenue is generated, a billed transaction needs to be created within receivables.

While creating an invoice with 'Invoicing Rules' as 'In Arrears' it is asking for 'Revenue Scheduling Rules' at line level. But our client doesn't want to give any revenue schedules.

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