Cross Ledger Payments (pay on behalf transaction by different legal entity/ledger)

Our client has multiple entities and requires data security across these entities. One of the entity (lets say A) , is responsible for processing some type of payments (i.e. large capex contracts) on behalf of all other entities (B1, B2, B3….Bn). This entity (A) is not a shared service entity, however rationale for processing such payment centrally is to ensure better control on large spends. This paying entity (A) operates bank account which is owned/managed by itself, however reserved for processing 'on behalf payments", while the entity (A) manages other bank accounts for its operational needs. Other entities (B1, B2, B3….Bn) fairly operates independently, except for these capex contracts.