Why is my On-Hire Invoice called a "Contract"?
When an invoice is On-Hire, the value is subject to change, for example, if the customer was to return early or late, or otherwise incur extra charges.
The price given to a customer at the start of the Hire may differ to the price at the end (Due to Early returns, Stand-downs etc).
As such, by default an On-Hire Invoice will display as a Contract until all the items on it are returned.
The core concern with supplying an official tax invoice during an on-hire period is that the customer may (rightly) consider it a final value, payable invoice.
The terminology "contract" assists with this, as it suggests that the total price is only valid if contract terms are followed (including the hire dates and the items). Any deviation from these will void the contract, and a new price can be expected.
Once an Invoice with a particular invoice number has been payed in full by a customer, it is hard (and arguably bad practice) to alter that invoice and re-send it to them demanding more money, as their records will indicate (correctly) that they have paid that Tax Invoice in full.