What to put in writing before the first payment
A booking paid in parts needs one record both sides can point at. Here is what belongs in it, and which line is always the one missing.
Why the record matters more than usual
When a price is paid once, the paperwork can be thin. An invoice, a receipt, and the thing either arrives or it does not. A booking paid in four parts across five months is a different object. It has four moments where what you believe was agreed and what your customer believes was agreed can quietly come apart, and the gap almost never shows up at the first one.
The written version is not for the dispute you are expecting. It is for the ordinary disagreement: a customer who remembers the final payment falling after the date rather than before it, or who understood the deposit to be the commitment and the rest to be an estimate. One page both sides can point at ends that conversation in a minute instead of an afternoon, and it ends it without either person having to be right about a phone call nobody wrote down.
The lines that do the work
Most of what belongs in the record is already in your head when you quote the price. Putting it in one place, in the words your customer would use rather than your internal shorthand, takes a paragraph. The two that get left out are always the last two, because they describe the week you are hoping not to have, and they are the only two anybody reads twice.
The total price as a single number, and plainly what it covers. The figure people check against later is the total, not the parts.
The amount taken today, and the fact that it is the first payment of several rather than a separate holding fee.
Every remaining amount with its own calendar date. All of them, written out, even when they are identical.
Which card will be charged, described the way the customer will recognise it, and that it is their own card throughout.
What happens when a payment does not go through: how many attempts you will make, how far apart they are, and who they should speak to.
What happens if they cancel: how much of what has already been paid comes back, and the point after which it stops coming back.
Say the dates, not the cadence
Monthly is not a date. It is a word that means the same day each month until it meets a month that has no thirty-first, and then it quietly means something else: a payment that lands early, or late, or on a day the customer was not watching their balance. Every four weeks is worse, because it drifts against the calendar all the way to a thirteenth payment and nobody can rebuild the list from the phrase. So write the dates. A schedule with five dates on it can be checked in five seconds by the person paying and by whoever covers your desk while you are away, and it settles in advance the question you would otherwise answer on the day: whether a payment due at the end of a short month was meant to arrive earlier or later than it did.
Who agreed, and what they saw
A schedule one person typed into a system is a plan. A schedule the customer agreed to, with their typed name, the moment they did it, and a copy of the exact wording they were shown, is a record. The second survives a staff change and an awkward email. The first is a note in a folder.
The wording part matters more than it sounds. Terms get edited: a fourteen-day rule becomes a twenty-one-day rule, a cancellation window moves, a sentence is tightened after a conversation you would rather not repeat. If you keep only the current version, you have lost the one your customer actually agreed to, and you will find yourself arguing about the page as it reads now over a booking made when it read differently. Store the text alongside the schedule, not instead of it.