Pick a real money product (Venmo, Cash App, Wise, Stripe Connect, Razorpay Route) and produce an architecture document that traces ONE money flow end-to-end — e.g. 'User A pays User B via Venmo'. Identify every layer (app → processor → scheme → banks → central bank), every settlement event, every reversibility window. Include a diagram and a list of the regulatory entities involved.
Pick a product you actually use — you'll have intuition about the UX, which helps map to the technical layers.
Don't try to cover all flows; pick ONE (e.g. P2P payment, deposit funding, card spending). Depth matters more than breadth.
Use real source docs: Stripe's docs, NACHA Operating Rules summary, EU PSD2 directive. Avoid speculation.
For Venmo specifically: it's PayPal's product → Bank Sponsor → PayPal Custodial Accounts → ACH for funding/withdrawal → card rails for spending.
Title: How Venmo Moves Money (P2P Transfer Flow)
Setup:
Alice has $100 Venmo balance (linked Chase checking; KYC verified)
Bob has Venmo account (linked BofA checking; KYC verified)
Flow: Alice sends Bob $50 via Venmo
Step 1: APP LAYER (instant)
Alice's app: deduct $50 from balance, add to "pending" outgoing
...
Step 2: PROCESSOR (PayPal): pre-funded balances
PayPal moves $50 from Alice's custodial holding to Bob's custodial holding
Both held at PayPal's sponsor bank (Synchrony Bank as of 2025)
...
Step 3: NETWORK: no external rails because pre-funded balance transfer
Internal balance reassignment only.
If Alice's balance was insufficient, fallback to:
- Linked debit card pull (instant; fee 1.75%)
- Linked bank ACH (T+1, free)
Step 4: BANKS: only triggered on cash-out
Bob keeps balance in Venmo: no rail
Bob "transfers to bank": ACH from PayPal's sponsor → Bob's BofA (T+1, free)
Bob "instant transfer": Visa/MC Push (instant, 1.75% fee)
Reversibility:
In-network (Alice → Bob): no chargeback; PayPal terms allow them to claw back fraud
Funding ACH source: R10 risk for 60 days; PayPal eats this loss (Alice's account)
Cash-out to Bob's bank: irreversible once ACH settles (T+1)
Regulatory:
PayPal: state-licensed money transmitter (US); FCA-regulated (UK)
KYC required at $300 cumulative (CTR threshold under BSA)
...