What a customer should see before they agree to a schedule
The screen where someone signs up for four dated payments is the whole arrangement. Here is what belongs on it, and what belongs behind a toggle.
One screen carries the whole arrangement
Someone agreeing to pay in instalments is agreeing to money leaving their account on dates that have not happened yet, for something they cannot hold yet. They will decide that in about forty seconds, on a phone, probably while doing something else. Then months pass. When the third payment lands and they ring you about it, what they are working from is not the agreement they ticked and not the email you sent: it is whatever they remember seeing on that screen. So the screen has to carry the arrangement on its own, and the parts that matter most cannot be the parts that need a click.
Four numbers, visible without a click
Before any explanation of how it works, a customer needs four amounts and dates in front of them, in this order:
The total price, the same number they saw on the thing they are buying and not a new one.
What leaves their card today, labelled as today and separated from the rest.
The remainder, written as a count, an amount and a cadence: four monthly payments of this much.
The date the last payment lands, written as a date.
The fourth is the line most pages leave out and the first thing customers ask about. A cadence is not a date. Monthly tells someone the rhythm and nothing about when they are finished, and a person who cannot see the end of a schedule will assume it is longer than it is. If you offer more than one shape of schedule, each option should carry its own first and last date rather than only a count, because choosing between four monthly payments and eight weekly ones is mostly a choice about when it ends.
The authorisation in a sentence they could repeat back
The tick box is the hinge of the page, so it deserves a written sentence rather than a label. Name yourself, name the dates, and say what is being allowed: I agree to the instalment agreement and authorise this business to charge my card on the dates above. Short enough to be read, specific enough to mean something. A tick beside the words I accept the terms records that a box was ticked and nothing about what the person understood.
What happens when a payment does not go through belongs on the same screen, in a line or two: the customer is emailed, the card may be retried, and a missed payment can be paid at once, spread across the later payments, or replaced by a new card. It is the most common question after a plan starts and it costs nothing to answer before it is asked. Answered later, inside a decline notice, the same words read like a rule you have just invented.
The agreement itself should be on the page rather than behind a link to another site, and it is fair to collapse it: the title and payment terms showing, the rest behind a read-more, so the signature box is never buried under text nobody scrolls. What matters is that the amounts inside the agreement are the amounts in the summary above it. In SPLTR's checkout they are filled from the same schedule for that reason, since an agreement quoting different figures from the page is worse than no agreement at all.
Signed means knowing who, when, and what they saw
A ticked box is not a signature and will not help you in a disagreement. Ask for a typed full name, treat that as the signature, and ask for an email for receipts in the same breath. Then keep, alongside the plan, the typed name, the date and time, the IP address, the browser it came from, and a hash of the exact text that was on screen. The hash is the part people skip and the part that settles things: if you ever reword your agreement, it proves which wording this customer agreed to.
Keep two things off the page. Any amount a customer meets for the first time after their card is saved — a fee, a rounding difference on the final payment, a charge attached to a retry — belongs in those four numbers or nowhere. And any field you do not need: a postal address for a registration, a phone number you will never dial. Then send the same screen as an email, dates and amounts and the sentence they agreed to, so the person reading their statement months later can answer their own question without calling you.