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Stripe API and SDK 23

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Module 1 · How a card payment works

Selling online means taking money from strangers

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1 / 171 · How a card payment works

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Selling online means taking money from strangers
Four parties and a card network take part in every card payment
, 1 to practiseCheck: who decides?
Authorisation asks; capture takes
, 1 to practisePractise: the life of a payment
, 1 to practisePayments cost a fee, and some fail
Cards are one way to pay among many
Recap

A processor connects your shop to the card world
Card numbers are dangerous to hold
, 1 to practiseCheck: who sees the card?
Your code talks to Stripe through its API
Everything in Stripe is an object with an id
, 2 to practisePractise: read an id
Two ways to take a payment with Stripe
Recap

Computers are bad at decimal fractions
Stripe counts money in the smallest unit
, 2 to practisePractise: amounts
, 1 to practiseCurrencies have codes, and some have no cents
Show prices with Intl.NumberFormat
, 1 to practiseRound once, on purpose
, 1 to practiseTry it: total a cart in cents
Recap

An account is free, and you can practise at once
Test mode is a copy of Stripe where no money moves
The Dashboard shows everything your code does
Two kinds of API key: publishable and secret
, 2 to practiseCheck: which key goes where?
Keep keys in environment variables
, 1 to practiseTest cards make every outcome happen on purpose
Recap

Three tools: a terminal, Node.js and npm
Make a project and install stripe
A client is your connection to Stripe
Check your work in the Dashboard
, 2 to practiseThe library mirrors the API
, 1 to practiseRead the error: it usually says what’s wrong
Stripe keeps a log of every request
Recap

A product says what; a price says how much
Make them in the Dashboard or in code
, 1 to practiseA recurring price bills again every period
, 1 to practiseA price’s amount never changes: make a new one
Lookup keys: names that work in every environment
, 1 to practiseOr describe the price inside each checkout
, 1 to practiseMetadata: your own labels on Stripe’s objects
Recap

A Checkout Session is one visit to a payment page
A small server to hang it on
Create the session
, 1 to practiseThe browser says what; the server says how much
, 1 to practiseLine items: a catalogue price or an inline one
, 1 to practiseSend the buyer with a 303 redirect
, 1 to practiseOptions worth knowing
Recap

Every checkout ends at one of two addresses
, 1 to practise{CHECKOUT_SESSION_ID} is filled in by Stripe
The success page asks Stripe what happened
, 1 to practiseVisiting the success page must grant nothing
, 1 to practiseTwo fields tell you where a session stands
, 1 to practiseTie the session to your own order
Line items come only when you ask
, 1 to practiseThe cancel page keeps the cart
Recap

A webhook is Stripe calling you
An event names what happened and carries the object
, 1 to practiseCheck: who tells the bakery?
Signatures prove an event really came from Stripe
A webhook endpoint in Express
, 1 to practiseVerify the exact bytes Stripe sent
, 1 to practiseTry it: compute a Stripe signature
, 1 to practiseTry it: verify a delivery
, 1 to practiseHandle each event type you care about
, 1 to practiseAnswer quickly, with the right status
Register the endpoint and keep its secret
Recap

The Stripe CLI brings Stripe to your terminal
, 1 to practisestripe listen forwards events to your laptop
stripe trigger makes an event happen
, 1 to practisePractise: a whole purchase on your laptop
Automated tests can sign their own events
, 2 to practiseTest the edges, not only the happy path
, 1 to practiseThe Dashboard shows every delivery
Recap

Events arrive at least once, and in any order
Let the database decide whether this is the first time
, 1 to practiseSpot the race
, 1 to practiseTry it: a handler that is safe to repeat
Or remember which events you’ve handled
, 1 to practiseRecord first, answer fast, do slow work later
, 1 to practiseDelayed payments: two events, one order
, 1 to practiseOne fulfilment function, called from two places
Recap

A Payment Intent follows one payment to the end
, 1 to practiseA Payment Intent moves through a few statuses
Your own form: the server makes the Payment Intent
The browser mounts the Payment Element and confirms
, 1 to practiseGuard the client secret
, 1 to practiseSome banks ask the buyer to prove it’s them
, 1 to practiseAuthorise now, capture later
Checkout or Elements?
Recap

, 1 to practiseA Customer remembers a buyer across payments
, 1 to practiseOne Stripe customer per person in your system
A subscription bills a customer every period
, 1 to practiseSell the bread club with Checkout
, 1 to practiseA subscription’s life, in statuses
, 1 to practiseTry it: decide access from the status
, 1 to practiseFollow subscriptions through their events
Where “paid until” lives
Recap

, 1 to practiseA free trial delays the first payment
, 1 to practisePlan for the end of the trial
Switch a member to another price
, 1 to practiseProration: paying fairly for part of a period
, 1 to practiseChoose when prorations are billed
, 1 to practiseCancel now, or at the end of the period
, 1 to practiseThe customer portal lets members manage themselves
Recap

An invoice goes from draft to paid
, 1 to practiseCheck: invoice statuses
, 1 to practiseWhat an invoice tells you
Renewals fail, and most can be saved
, 1 to practiseHandle a failed renewal in your webhook
, 1 to practiseWhen retries run out
, 1 to practiseBill a business by invoice
Recap

A refund gives back all or part of a payment
, 1 to practiseRefunds arrive as events, whoever made them
A dispute is the buyer’s bank taking money back
, 1 to practiseRespond with evidence, or accept it
Taxes, in general terms
, 1 to practiseStripe Tax works out the amount at checkout
, 1 to practiseRead what was charged
Recap

A request can fail in three different places
Every Stripe error has a type and a status
, 1 to practiseCatch the errors you mean
, 1 to practiseCard errors are for the buyer, gently
An idempotency key makes a retry safe
, 2 to practiseDerive the key from what the request is for
, 1 to practiseTry it: retry with one key
, 1 to practiseLet the library retry for you
Recap

Your database mirrors Stripe; it doesn’t compete with it
, 1 to practiseEvents don’t arrive in order
Treat an event as a nudge, and fetch the truth
, 1 to practiseCatch up on events you missed
, 1 to practiseA regular check catches what events miss
Follow the money: balance, transactions, payouts
, 1 to practiseReconcile a payout line by line
Recap

Fraud costs the merchant
, 1 to practiseRadar scores every payment
, 1 to practiseRules and reviews tune Radar to your shop
, 1 to practiseEarly fraud warnings: refund before the dispute
, 1 to practiseMake your checkout a poor target
, 1 to practiseA security review of a payment flow
, 1 to practiseGoing live
Recap

The brief: review the bakery’s payments
, 1 to practiseChallenge: the whole one-off flow
, 1 to practiseChallenge: the handler that emails twice
, 1 to practiseChallenge: nobody can join the trial
, 1 to practiseChallenge: the upgrade that doubled the bill
, 2 to practiseChallenge: a safe refund from a queue
, 1 to practiseChallenge: the member who came back from the dead
, 2 to practiseChallenge: launch day
, 1 to practiseChallenge: one last route
Recap: what an expert checks