agentic payments infrastructure

The technical reference
for AI-native payments

Deep dives into Visa Intelligent Commerce, Trusted Agent Protocol, ISO 8583 modifications, and the full stack of protocols that let AI agents pay for things autonomously.

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Writing
01
live TAP VIC ISO 8583 x402
How an AI agent buys something: the complete technical breakdown
HTTP signatures, agent-bound tokens, ISO 8583 field modifications, the VIC API sequence, and the protocol landscape across TAP, x402, and AP2. Four interactive diagrams.
Mar 21, 2026 · 18 min read
Diagrams
architecture overview
TAP handshake
ISO 8583 anatomy
02
live Visa Mastercard 4-party Agent Pay
The 4-party model for AI payments: how Visa and Mastercard rebuilt the rails
How each role changes when an AI agent initiates the transaction — and how the two networks chose different architectures for the same problem. Three interactive diagrams.
Apr 4, 2026 · long read
Diagrams
authorization flow
fraud layers
rebuild map
03
Apr 18 · coming soon
ISO 8583 for agents: the complete field reference
Every modified field, valid values, how issuers interpret F022=81, and what T+1 clearing looks like for agent transactions.
ISO 8583 F022=81 MTI 0220
04
May 2 · coming soon
The Trusted Agent Protocol spec, line by line
Ed25519 key registration, nonce store design, the 60-second window, and why replay protection is harder than it looks.
TAP spec Ed25519 RFC 9421
05
May 16 · coming soon
x402 in depth: HTTP-native payments for agents
The payment flow, facilitator architecture, V2 spec changes, and when to use x402 over TAP.
x402 USDC Base / Solana
Why this exists
01
The documentation gap is real
Visa's VIC sandbox has 30+ active partners. None of them has published a clear explanation of how ISO 8583 changes for agent transactions. This is that resource.
02
Diagrams as primary source
Every post ships a new interactive diagram built with payarch. The architecture is the explanation — text annotates what the diagram already shows.
03
Written by someone building it
Not summarized from press releases. The protocol analysis comes from reading the specs, the GitHub repos, and the primary documentation — then explaining it clearly.
About
Iñigo
Software Engineer
payarch is a project to map the architecture of the AI agent payments ecosystem — the protocols, the rails, and the infrastructure being built right now.

Each post ships a new interactive diagram. The goal is simple: make this space legible to the engineers and founders building in it.
ivalenzuelan vn.inigo@gmail.com
2
Posts published
12
Posts planned
6
Diagrams shipped
2026
Project started