# Apiosk Gateway – On-Chain Reserve Attestation (Base)

> Apiosk Gateway – On-Chain Reserve Attestation (Base) is a paid API for AI agents from gateway.apiosk.com, paid per call via x402, $0.03/call, status unknown (last checked 2026-09-16).

Reads the ERC-20 balanceOf for a given token/holder pair on Base at the current block and returns the balance with a JWS-HS256 signed receipt that includes the exact eth_call parameters for independent verification.

## Facts

- Endpoint: POST https://gateway.apiosk.com/attestations/onchain-reserve
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/apiosk-gateway-on-chain-reserve-attestation-base-4bf5ac11
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2jOXS-qVITrWVIkAmOrY7

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 apiosk-gateway-on-chain-reserve-attestation-base-4bf5ac11 -d '<json body>'
```

Example prompt: Can you get me a signed on-chain attestation of how many USDC tokens the wallet 0xAbC...123 holds right now on Base — I need a verifiable JWS receipt I can share with an auditor?

## When to prefer this

Choose this endpoint when you need a cryptographically signed, independently verifiable proof of an ERC-20 token balance on Base — not just a raw balance read. It is ideal for audit trails, reserve attestations, compliance snapshots, or any scenario where a third party must be able to verify the result without trusting the caller. It is not suitable if you only need an unsigned balance for internal logic, or if you are querying chains other than Base.

## Known failure modes

- Invalid or non-ERC-20 contract address returns an error or zero balance
- Wallet address not checksummed or malformed causes a 400-level error
- Temporary Base RPC unavailability may cause a timeout or 503
- Payment not completed via x402 results in HTTP 402 response
- Block reorg between call and receipt delivery could cause minor inconsistency

## How this service works

Read balanceOf for a token/holder pair on Base at the current block and return the balance with a signed JWS-HS256 receipt. The envelope carries the exact eth_call (contract, calldata, block) so anyone can re-run it against any Base node.

## Output

A JSON response containing the current ERC-20 token balance for the specified holder, wrapped in a JWS-HS256 signed envelope. The envelope includes the exact eth_call parameters (contract address, calldata, block number) so any third party can independently re-run the query against any Base node to confirm the result.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/apiosk-gateway-on-chain-reserve-attestation-base-4bf5ac11/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from gateway.apiosk.com](https://www.zero.xyz/host/gateway.apiosk.com/llms.txt)