Configuration steps:-

• transaction VD02 - Change Customers – tick Billing and filled in the Customer Code, Sales org., Distr.channel and Division then hit enter.
• Look for field name Inv.list sched. – you must filled in the Factory Calendar that you are currently using.
• You can simulate the collective billing in transaction VF04 - Process Billing Due List.

During simulation, if the billings cannot be combine, the system will give you this message,

Different header fields $000000001 $000000002
Combination criteria in the billing xxxxxxxxxxxx123 xxxxxxxxxxxx125

Criteria to satisfy for collective billings:-

• Billing document type is the same.
• Reference document type is the same.