How should a client with an active subscription bill for an additional item they want to purchase ad hoc?

Billing for an additional item in an active subscription can effectively be managed by adding an additional line item to the existing invoice. This method maintains the integrity of the client's account by consolidating charges into a single invoice. It simplifies the billing process for both the client and the business, as clients prefer to have all charges grouped together, which also reduces administrative overhead in managing multiple invoices.

The option of creating a separate invoice could lead to confusion for the client, as they would have to manage and track multiple invoices for one subscription period. Charging the item directly to the credit card, while possible, may not provide a clear, itemized view of recurring subscription charges alongside ad-hoc purchases, which is often preferred for transparency and record-keeping. Waiting until the next billing cycle would delay the transaction for the client, which might not be ideal if they want the item immediately.

By adding the item as an additional line in an existing invoice, the billing reflects the subscription's current status and the new purchase in a clear and concise manner, ensuring a smoother experience for the client.