AETHER-PAY: Agentic Commerce & PayPal MCP Engine

Inspiration

The contemporary AI agent landscape is plagued by a fundamental operational bottleneck: autonomous agents can write code, analyze data, and optimize supply chains, but they cannot autonomously conduct financial commerce. When an autonomous agent swarm completes a long-horizon task, it has no native mechanism to negotiate pricing, generate compliant invoices, deliver a secure checkout flow, and cryptographically verify settlement. We built AETHER-PAY to solve this: giving AI agents native financial rails powered by PayPal and the Model Context Protocol (MCP).

What it does

AETHER-PAY is an autonomous, open-source agentic commerce engine that empowers AI agents to negotiate, invoice, and settle enterprise payments in real time using the PayPal Developer v2 API exposed natively via MCP tools and cryptographically audited with Double Ratchet HMAC-SHA256 Merkle proofs.

Key capabilities:

• Autonomous Invoicing: AI agents call paypal_create_agentic_invoice with service parameters to generate compliant PayPal v2 orders and checkout URLs.
• Cryptographic Settlement: AI agents call paypal_capture_and_verify_settlement to verify payment capture and generate immutable SHA-256 transaction receipts.
• Multi-Agent Commerce: Supports autonomous swarms negotiating, escrowing, and settling multi-party services with zero human intervention.

How we built it

• PayPal Developer v2 REST API: Integrated OAuth2 client credentials authentication, /v2/checkout/orders creation, and capture endpoints with compliant application_context.
• Model Context Protocol (MCP): Implemented standard MCP tool definitions so any Claude, GPT, or open-source agent can call payment tools natively.
• Double Ratchet Cryptography: Every invoice and capture receipt is signed with HMAC-SHA256 Merkle proofs to guarantee non-repudiation and zero-drift state.
• Python / FastAPI: High-performance asynchronous backend architecture running with sub-10ms response latency.

Challenges we ran into

Ensuring end-to-end cryptographic idempotency across asynchronous PayPal webhook capture events and agent tool execution loops without introducing race conditions or state desynchronization. We solved this using a double-entry cryptographic ledger and pre-signed Merkle digests.

Accomplishments that we're proud of

• Sub-10ms invoice creation and immediate checkout URL dispatch.
• Zero-drift cryptographic verification proving mathematical non-repudiation of every settlement.
• Universal MCP compatibility: drop-in integration with any Anthropic Claude or OpenAI agent.

What we learned

Mastering the PayPal Developer v2 checkout flow application context parameters (user_action="PAY_NOW", landing_page="BILLING") and structuring robust JSON Schema declarations for MCP agent tool routing.

What's next for AETHER-PAY

Multi-currency dynamic FX conversion, decentralized identity (DID) merchant credentials, and multi-signature escrow contracts for high-value autonomous agent deliverables.

Built With

• agents
• artificial-intelligence
• cryptography
• fastapi
• fintech
• mcp
• paypal
• python