How companies organize legal entities and organization structured is many and varied. If you have an environment with many legal entities that each do invoicing to the customer but the payment receipt is handled centrally then AX has some capabilities to setup processes. This video gives you a quick walk through of the concepts.
If you want some background of the setup then this video will walk through the setup prior to being able to process the invoices in the payment.
This video was recorded with AX2012 R2 but the same concepts apply to any release of AX2012.