Fundamentals
The fundamentals. Unpacked.
The vocabulary of money, explained properly. No jargon, no hand-waving, no assumed knowledge. Each one takes about three minutes and leaves you able to hold your own in the room.
Start here
A reading path through the whole thing.
Ten pieces, about 27 minutes. Short route: four pieces, about 11 minutes.
Four is the minimum. Ten is the full tour. Read them in this order and the rest of the library stops being a list of terms.
- Issuer, acquirer, processor: who is who?short route
- What happens when you tap a card?short route
- What is a payment gateway?short route
- What is settlement?short route
- What is interchange?
- How do bank codes work? (IFSC, swift/bic, IBAN)
- What is KYC?
- What is a chargeback?
- Why do payments fail?
- What is a payment aggregator?
100 of 100 shown
The rails · 27
The systems that actually move money between accounts.
- For everyone
What is UPI?
Not a wallet. A public layer letting any app move money between any two bank accounts instantly and for free.
2 min read - For everyone
What happens when you tap a card?
A card payment is three separate events on three different clocks. The beep is a promise, not a payment. Here is the full sequence.
2 min read - For everyone
What is SWIFT?
SWIFT is a messaging network, not a payment network. It has never moved money.
2 min read - For everyone
What is settlement?
The exact moment money actually moves between institutions.
3 min read - For everyone
Issuer, acquirer, processor: who is who?
Four institutions touch every card payment and everyone confuses their names.
3 min read - For everyone
What is a stablecoin?
A digital IOU pegged to a currency and issued by a private company.
3 min read - For everyone
NEFT, RTGS, IMPS and UPI: what is the difference?
Four domestic payment rails, four different jobs.
2 min read - For everyone
What is a wallet (and what is a PPI)?
A wallet holds money; a bank account holds money differently. The difference is what protects you.
2 min read - For everyone
How do bank codes work? (IFSC, swift/bic, IBAN)
IFSC, SWIFT, BIC, IBAN, routing number. Different codes for different jobs.
2 min read - For everyone
What are nostro and vostro accounts?
Your money never crosses the border.
3 min read - For everyone
What is SEPA, and why is Europe different?
SEPA turned forty-one countries into a single domestic payment area for the euro.
2 min read - For everyone
What is a QR code payment (static versus dynamic)?
A QR code is not a payment method. It is an address.
3 min read - For everyone
What is ACH, and why is it so slow?
ACH moves most money in America, and it still runs on batches designed in the 1970s.
2 min read - For everyone
ACH or wire: which one, and why the price is so different
One costs pennies and takes days. The other costs thirty dollars and takes minutes.
2 min read - For everyone
How does tap to pay actually work?
Apple Pay and Google Pay do not send your card number to the shop.
3 min read - For everyone
What are real-time payments (FedNow, RTP, and the instant era)?
Instant rails settle in seconds, around the clock, in central bank money.
2 min read - For everyone
Why do cheques still exist, and how long do they really take?
America still writes billions of cheques a year.
2 min read - For everyone
How does an ATM actually work?
The machine dispensing your cash is often not owned by your bank, and the notes inside belong to somebody else entirely.
2 min read - For everyone
What is account-to-account payment, and why do merchants want it?
Account-to-account payment moves money between banks with no card in the middle.
3 min read - For everyone
What is a UTR number (and what is an ARN)?
A UTR is the tracking number for a bank transfer, and an ARN is the one for a card refund.
3 min read - For everyone
What is UPI Lite, and how does it work without the internet?
UPI Lite keeps a small balance on your phone so small payments skip the bank entirely. Here is what that buys, and what you give up.
3 min read - For everyone
What is an MT103, and how do you trace an international payment?
An MT103 is the message that carries an international transfer, and the document that lets you trace one.
3 min read - For everyone
What is a card scheme, and how do Visa and Mastercard make money?
Visa and Mastercard do not issue cards, do not lend, and do not hold your money.
2 min read - For everyone
What is a CBDC (and is the digital rupee different)?
A central bank digital currency is not the money in your bank account.
2 min read - For everyone
What is a correspondent bank?
A correspondent bank is another bank's account holder abroad.
3 min read - For builders
What is ISO 20022, and why did every bank have to change?
ISO 20022 replaced free-text payment messages with structured data.
3 min read - For everyone
What is Aani, and how does the Gulf do instant payments?
Aani is the UAE's national instant payments platform.
3 min read
The money · 23
How value moves, gets priced, and lands somewhere.
- For everyone
What is interchange?
The fee inside the fee: the slice of every card payment that flows back to the cardholder's bank.
3 min read - For builders
What is reconciliation?
Reconciliation is matching what you think happened against what actually happened.
3 min read - For builders
What is a payout?
A payout is money going out rather than coming in, and it is a completely different technical problem.
3 min read - For everyone
What is no-cost EMI, and who pays for it?
No-cost EMI is not free credit.
2 min read - For everyone
What is currency conversion, and what is DCC?
Every currency conversion has a real rate and a rate you were given. The gap is the fee.
3 min read - For everyone
What is remittance, and why does it cost so much?
India receives more remittances than any country on earth.
2 min read - For everyone
What is MDR (merchant discount rate)?
MDR is the fee a merchant pays to accept your payment. Here is who it splits between, and why India made part of it zero.
2 min read - For everyone
What is float, and who earns it?
Between the moment you pay and the moment money arrives, it sits somewhere.
2 min read - For builders
What is a rolling reserve?
Your payment provider is holding back a percentage of your revenue. It is not a penalty and it is not a scam.
2 min read - For everyone
What is APR, and why is it not the interest rate?
APR is meant to be the one number you can compare across lenders.
3 min read - For everyone
How does a bank actually make money?
Not from your monthly fee.
3 min read - For everyone
What is an overdraft fee, and why is it so expensive?
A flat fee for a tiny shortfall is the most expensive short-term credit most people ever use.
2 min read - For everyone
What is an FX spread, and how is the mid-market rate actually set?
The mid-market rate is a midpoint nobody actually trades at.
3 min read - For builders
What is a scheme fee, and how is it different from interchange?
Interchange goes to the issuing bank. Scheme fees go to Visa and Mastercard.
3 min read - For everyone
What is the minimum due on a credit card, and what does paying it cost?
Paying the minimum keeps your account current and your debt growing.
3 min read - For everyone
What are OUR, BEN and SHA charges on an international transfer?
Three codes decide who pays the fees on an international transfer, and one of them is why the recipient got less than you sent.
3 min read - For everyone
What is a credit limit, and what is credit utilisation?
Your credit limit is what you can borrow.
3 min read - For everyone
What is a forex card, and is it better than your debit card abroad?
A forex card locks your exchange rate before you travel.
3 min read - For everyone
What is EMI on a debit card?
Debit card EMI is a pre-approved loan attached to your bank account, not a card feature.
2 min read - For everyone
What is netting, and why do banks not settle every payment?
Millions of payments settle as a handful of transfers. Here is how netting works, what it saves, and the risk it quietly creates.
3 min read - For everyone
What is BNPL, and who is actually lending?
Buy now pay later looks like a payment method and behaves like a loan.
2 min read - For everyone
What is a merchant category code, and why does it decide so much?
A four-digit code decides your rewards, your fees, and sometimes whether a payment is allowed at all.
3 min read - For builders
What is card-not-present, and why does it cost more?
Typing a card number costs the merchant more than tapping it.
2 min read
Trust and risk · 29
Who is allowed to pay, and what happens when it goes wrong.
- For everyone
What is KYC?
The checkpoint that decides whether the financial system will trust you, run on the regulator's behalf.
3 min read - For everyone
What is a chargeback?
Not a refund. Your bank reaching through the card network to reverse a payment, whether the merchant agrees or not.
2 min read - For everyone
What is card tokenization?
Tokenization replaces your card number with a meaningless substitute so merchants never store the real thing.
2 min read - For everyone
What is 3D secure, and why do I get an OTP?
That OTP screen is a protocol shifting fraud liability from the merchant to the bank.
2 min read - For builders
What is PCI DSS compliance?
The security standard every business touching card data must meet.
2 min read - For everyone
Refund, void, and reversal: what is the difference?
Three different ways money comes back, on three different timelines.
3 min read - For everyone
What is a credit score, and what is CIBIL?
A credit score predicts one thing only: whether you repay.
2 min read - For everyone
What is a fraud engine?
Every transaction is scored in milliseconds before approval.
2 min read - For everyone
What is AML, and how is it different from KYC?
KYC asks who you are, once. AML watches what you do, forever. Confusing the two is the most common mistake in financial compliance.
2 min read - For everyone
Why do payments fail?
A failed payment has one of about five real causes. The message on screen almost never tells you which, and that is a design choice.
3 min read - For everyone
What is FDIC insurance, and what does it not cover?
FDIC insurance covers your deposit if your bank fails.
2 min read - For everyone
What is a virtual card?
A virtual card is a real card number that exists only digitally, often for one merchant or one purchase.
3 min read - For everyone
Debit or credit: what actually changes
The two cards look identical and behave completely differently.
3 min read - For everyone
How does card fraud actually happen?
Not by guessing your PIN.
2 min read - For everyone
What is a bank run?
A bank run is not caused by a bank being broke. It is caused by everyone deciding at once that it might be.
2 min read - For builders
What is friendly fraud, and why do merchants fear it most?
The customer received the goods, then disputed the charge.
3 min read - For everyone
What is a soft decline, and why did my card work the second time?
A soft decline is a temporary no that invites a retry.
3 min read - For builders
What is KYB, and how is it different from KYC?
KYB is verifying a business rather than a person.
3 min read - For everyone
What is a CVV, and why is it not stored anywhere?
The three digits on the back of your card exist to prove you are holding it.
3 min read - For builders
What is a letter of credit?
A letter of credit lets two companies who do not trust each other trade anyway.
3 min read - For builders
How do you fight a chargeback?
Representment is how a merchant disputes a chargeback and asks for the money back.
3 min read - For everyone
What is APP fraud, and can you get the money back?
In APP fraud you sent the money yourself, which is why recovery was almost impossible.
3 min read - For everyone
What is confirmation of payee?
The check that asks whether the account name matches.
3 min read - For everyone
What is a money mule?
A money mule moves criminal funds through their own account.
3 min read - For everyone
Why do banks freeze accounts?
A freeze is usually a pause for review, not an accusation.
3 min read - For everyone
What is social engineering?
Social engineering attacks the person, not the system.
3 min read - For everyone
What is an authorisation hold?
The petrol pump blocked more than you spent.
2 min read - For builders
What is PSD2, and what changes with PSD3?
PSD2 forced European banks to open their data and add a second factor. PSD3 and the PSR tighten both.
4 min read - For builders
What is a chargeback ratio, and what happens when you breach it?
Card schemes monitor how often merchants get disputed. Cross the line and the consequences escalate fast.
3 min read
Building on it · 21
Pieces you assemble when you build a payments product.
- For everyone
What is a payment gateway?
The translator between a checkout page and the banking system.
3 min read - For builders
What is a payment aggregator?
Thousands of merchants can accept payments without each getting their own bank relationship.
3 min read - For builders
How do recurring payments actually work?
Subscriptions run on mandates, standing permissions you grant once.
2 min read - For builders
What is an escrow or nodal account?
When a platform holds money between buyer and seller, it must sit somewhere specific.
2 min read - For builders
What is open banking (and India's account aggregator)?
For a century your transaction data was visible only to your own bank.
3 min read - For builders
What is payment orchestration?
One payment provider is a single point of failure. Orchestration is the layer routing between several.
2 min read - For builders
What is a webhook, and why do payments need them?
A webhook is how a payment provider tells your system that something happened. Get them wrong and you ship goods for free.
2 min read - For builders
What is a merchant of record?
The merchant of record is whoever is legally selling to the customer.
2 min read - For builders
What is a virtual account?
A virtual account is a real account number that is not a real account.
2 min read - For builders
What is idempotency, and why do payments break without it?
A retried payment request must not create a second payment.
3 min read - For builders
Why do fintechs need double-entry bookkeeping?
A balance column in a database is not a ledger. Here is why money systems use double entry, and what breaks the moment you do not.
3 min read - For builders
What is a BIN, and what is BIN sponsorship?
The leading digits of a card say who issued it.
4 min read - For builders
What is a virtual IBAN?
A virtual IBAN is an account number that routes into a real account.
3 min read - For builders
What is a billing descriptor?
The billing descriptor is the text on a customer's statement.
3 min read - For builders
What is a direct debit mandate?
A mandate is standing permission to pull money from an account.
3 min read - For builders
What is a standing instruction?
A standing instruction pushes money on a schedule. A mandate lets someone pull it. The difference decides who controls the amount.
3 min read - For builders
What is hosted checkout, and how is it different from embedded?
Hosted checkout sends the customer to the provider. Embedded keeps them on your page.
3 min read - For builders
How does a fintech actually get licensed?
Building the product is the fast part.
2 min read - For builders
What is a payment facilitator (PayFac), and how is it different from an aggregator?
A payment facilitator holds one merchant account and puts many businesses underneath it.
3 min read - For builders
What is banking-as-a-service, and who is actually the bank?
Banking-as-a-service lets a company offer accounts without being a bank.
3 min read - For builders
What is involuntary churn, and why do subscriptions die at the payment step?
Most subscription cancellations are not decisions. They are failed payments nobody retried properly.
3 min read
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