For buyers contracting authority
Choose 48444100 when the package's main job is producing invoices and tracking what is owed, not keeping the general ledger. A consumption-based utility bill, a service-charge run, or a membership and discounts scheme points here; a full accounting back office points to the parent Accounting system (48444000).
The boundary that trips authorities is exactly that parent split. If the contract centres on the ledger, reconciliation and statutory reporting, code it as accounting; reserve the billing code for the rating-and-invoicing layer even when it feeds into the accounts. Where a single procurement bundles both, set the primary CPV code by the dominant deliverable, not the whole package.
Watch the ERP overlap too. When billing arrives as one module inside a broader enterprise resource planning rollout, the contract often gets a wider software code instead, so check whether billing is the purpose or just a part.