# LiquProp API - Gas-Free Polygon Payment Relay

> LiquProp API - Gas-Free Polygon Payment Relay is a paid API for AI agents from api.relai.fi, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Submits a gas-free blockchain payment transaction on Polygon, with RelAI sponsoring the transaction fees

## Facts

- Endpoint: POST https://api.relai.fi/relay/1776502063891/v1/
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/liquprop-api-f5376afe
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_8yllCgNdrg84po5RsbTfY

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability liquprop-api-f5376afe -d '<json body>'
```

Example prompt: Submit a gas-free payment on the Polygon network using LiquProp's RelAI relay — I need to send 5 USDC to wallet address 0xABC123... and I don't want to worry about MATIC for gas fees.

## When to prefer this

Choose this endpoint when you need to execute a payment on the Polygon blockchain but want to avoid requiring the sender to hold MATIC for gas fees. Ideal for applications onboarding new crypto users who may not have native gas tokens, or for automating payment flows where gas cost unpredictability is a concern. Preferred over direct on-chain submission when seamless UX and fee sponsorship are priorities.

## Known failure modes

- Insufficient USDC balance to cover the $0.01 relay fee — returns payment required error
- Invalid recipient wallet address — returns validation error
- Polygon network congestion causing relay timeout
- Transaction already submitted (duplicate nonce) — returns conflict error
- Relay quota exceeded for the calling account

## How this service works

Gas-free payment - RelAI sponsors transaction fees on polygon

## Output

Returns a relay confirmation containing the Polygon transaction hash and gas sponsorship details, confirming the transaction was broadcast to the network with fees covered by RelAI.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/liquprop-api-f5376afe/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.relai.fi](https://www.zero.xyz/host/api.relai.fi/llms.txt)