A: When you hire a vehicle on account (assuming you are not receiving any money immediately), you don't need to add or 'record' a tendered amount to start with. Once the account is paid, you would receive this money in your financial system and then record this receipt in RCM.
To record the receipt in RCM and allow you to close the booking (it will now have a zero balance),you can create an On Account tender type. This groups the 'on account' payments into a separate total which is shown separately from your other 'cash' bankings. Note that total bankings will always be calculated net of the On Account tender type.
To add the On Account Tender Type, just go System Setup, click Tender Types, then add the On Account record there.