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By REAPP - Real Agentic Payments Protocol
In the words of the Stellar Foundation, "Galaxy estimates that agentic commerce could represent $3-5 trillion in B2C revenue by 2030." However, even after the implementation of x402, agentic commerce is still impossible on Stellar.
REAPP is a developer SDK and smart contract system that enables agentic payments on Stellar, with authorization, spending enforcement, and audit built into every transaction. A user signs a mandate once, defining what an agent is allowed to spend. From that point, the agent operates autonomously within those bounds, with every payment authorized, enforced, and recorded on-chain.
## Components and Stellar usage
REAPP SDK. A single function call, agent.fetch(), gives developers authorized agentic payments on Stellar. The SDK handles mandate validation, spending policy checks, and x402 settlement under the hood. Stellar usage: uses Stellar's native XDR format and fee-bump sponsorship. Impact: the SDK wraps mandate validation and Soroban enforcement into the same agent.fetch() call, so the developer-facing API stays as simple as a standard x402 integration.
Soroban MandateRegistry. Smart contract enforcing per-agent spending policies on-chain: budget caps, period limits, merchant restrictions. A misbehaving agent cannot bypass it. Stellar usage: runs on Soroban, the same chain where x402 settles, so enforcement and settlement share a single trust boundary. Impact: spending limits are protocol-enforced rather than application-enforced — an advantage no EVM agentic payment project has. Upgrades are gated by a 2-of-3 multisig held by the founding team with a timelock so any change is visible before it takes effect. The final mainnet version ships without an upgrade function and is fully immutable. Any future update deploys as a new contract while existing mandates on the original execute to completion.
AP2 mandate engine. TypeScript implementation of Google's AP2 spec — no other production implementation exists. Users sign credentials defining what an agent can spend. REAPP injects mandate validation into the x402 flow, so no payment proceeds without verified user authorization. Stellar usage: gates x402 settlement on Stellar with cryptographic proof of consent. Impact: closes the authorization gap that x402 leaves open.
All Soroban contracts and SDK packages developed under this award are open-sourced under Apache-2.0
$70.0K
We built Query402 (https://query402.xyz), a live x402 merchant on Stellar testnet that takes real USDC payments per HTTP request, with no API keys, no accounts, and no human in the loop. It implements the full x402-on-Stellar settlement loop end-to-end using the official @x402/core, @x402/express, @x402/fetch, and @x402/stellar v2.9 packages, with ExactStellarScheme, ed25519 signing via createEd25519Signer, and the OpenZeppelin Channels facilitator handling verification and settlement. The system issues 402 challenges, accepts signed payment authorizations, settles on-chain in seconds, and persists PAYMENT-RESPONSE receipts with transaction hashes for every paid request. On top of that primitive, Query402 includes an autonomous research agent that pays per reasoning step in USDC, it plans queries, pays for each one, evaluates its own coverage, pays for refinement searches if evidence is thin, and synthesizes a final report.
Query402 showcases the x402-on-Stellar settlement layer of the REAPP composition, deployed and processing real testnet payments today. The autonomous agent inside Query402 is exactly the kind of consumer REAPP exists to authorize. Right now it spends from a hot key with no policy enforcement, which is the gap REAPP closes.
Ship a working end-to-end flow on testnet: user signs mandate, agent pays for a resource via x402, Soroban enforces the spending limit.
MandateRegistry Soroban contract deployed on testnet — $9,600 (120hrs)
Contract live on testnet with register_mandate, validate_and_consume, execute_payment, and revoke_mandate callable. Integration tests passing, including negative cases for unauthorized callers and overspend attempts.
@reapp/sdk core package published to npm — $3,600 (45 hrs)
Package installable via npm. Developer can create an agent, connect to the testnet contract, and execute a mandate-validated payment in under 10 lines of code.
x402 testnet payment round-trip working end-to-end — $1,600 (20hrs)
Agent.fetch(url) receives 402, validates mandate, signs XDR, pays, receives resource. Reviewer can reproduce the full ResearchAgent scenario on testnet using the SDK.
Total: 14,800
Expand from a single flow to a complete developer toolkit. External developers can install the SDK and run the demo on testnet.
SDK packages published on npm: @reapp/express-middleware, @reapp/stellar, @reapp/ap2 — 7,200 (90hrs)
Three packages installable and typed. Each has API docs and usage examples in README. Reviewer can npm install and import without errors.
CLI tool with init, setup, mandate create, pay, and demo commands — $4,800 (60hrs)
Reviewer can run npx reapp-cli demo research-agent on testnet and see a complete payment flow in terminal.
Reference consumer and fulfillment agents — $4,800 (60hrs)
Two working example agents in the repo: consumer pays for data via agent.fetch(), fulfillment serves a 402-gated Express API. Both run on testnet with a single setup command.
AP2 compliance validator with test suite — $7,600 (95hrs) Validator checks signature, merchant scope, amount, expiry, and replay. Test suite with 20+ cases covering valid mandates, expired mandates, wrong merchant, overspend, and replayed mandate hashes.
Total: 24,400
MandateRegistry deployed on Stellar mainnet - $8,800 (110hrs)
Contract deployed on mainnet with OpenZeppelin access control, 2-of-3 multisig gating upgrades, and timelock on contract changes. Signature coordination tooling for the team to execute upgrades. Contract ID published in SDK config. Reviewer can execute a real USDC payment through the full REAPP flow on mainnet.
Contract security test suite and verification - $13,600 (170hrs)
Every contract function has passing negative tests for unauthorized callers, expired mandates, overspend attempts, replay attacks, and unauthorized upgrade attempts. Threat model covering identified attack surfaces and mitigations reviewed and merged. Data flow diagrams documenting trust boundaries and data entities across the mandate lifecycle. Security scanning with results published in the repo. All findings remediated. Repository structured and documented so an external reviewer can navigate the codebase, run tests, and verify contract behavior independently.
SDK, CLI, and reference agents operational on mainnet — $3,200 (40 hrs)
All SDK packages and CLI commands work on mainnet. Reference consumer and fulfillment agents from T2 operational on mainnet with real USDC. Reviewer can run npx reapp-cli demo research-agent --network mainnet and complete a real payment.
Web wallet and consumer demo app — $5,200 (65hrs)
User can sign an IntentMandate, register it on Soroban, and interact with an AI agent that makes mandate-validated payments through a chat interface. Built with Vercel AI SDK and assistant-ui. Reviewer can complete the full flow — from mandate signing to autonomous agent payment — using the hosted app on mainnet.
Total: 30,800
Alex Astrum Protocol Architect - Agentic AI expert with 20+ years of full-stack engineering experience, currently at Google on the Antigravity team within the Gemini ecosystem. Contributor to Firebase. Leads REAPP's spec design and SDK architecture.
LinkedIn: https://www.linkedin.com/in/alexastrum/?originalSubdomain=ca GitHub: https://github.com/alexastrum
Drew Raines Engineering Lead - Shipped smart contracts and production systems across eight chains including Ethereum, Solana, Bitcoin, and Cosmos. Built an NFT marketplace engine, a decentralized social network on Polygon mainnet, and a Bitcoin ordinal inscription engine with escrow wrapping on ICP. Leads REAPP's Soroban contract implementation and x402 Stellar integration.
LinkedIn: https://www.linkedin.com/in/drew-raines-19831072/ GitHub: https://github.com/futurehelp
Max Shama Product & Ecosystem Lead - Led the development of agentic blockchain products across NEAR and Avalanche, including DeFi agents and custom AI agent frameworks. Previously a chair in NEAR NDC overseeing ecosystem grant allocation. Leads REAPP's product direction and ecosystem partnerships.
Alex
Max Shama
By REAPP - Real Agentic Payments Protocol
REAPP: x402 Agentic Payments on Stellar