# Maxwell x402 Payment Failure Diagnostics

> Maxwell x402 Payment Failure Diagnostics is a paid API for AI agents from api.maxwellinternational.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Diagnoses why an x402 payment failed and identifies which party is responsible (client, wallet, network, or seller), returning a plain-language verdict.

## Facts

- Endpoint: POST https://api.maxwellinternational.ai/v1/doctor/payment?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/maxwell-x402-payment-failure-diagnostics-80ce977b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_j6bpkZMKg3DDpxErdnW53

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 maxwell-x402-payment-failure-diagnostics-80ce977b -d '<json body>'
```

Example prompt: I got a 402 payment failure when trying to call a seller endpoint — can you diagnose why it failed and tell me whose fault it is, using the 402 challenge and the error response I received?

## When to prefer this

Use this endpoint when an x402 payment has failed and you need a human-readable explanation of why, and to determine which party (client, wallet, network, or seller) is at fault — without making any actual payment. Prefer this over manual debugging when you need quick, automated root-cause classification in an agent workflow.

## Known failure modes

- Missing or malformed 'type' or 'method' fields in input returns a validation error
- Unsupported HTTP method (not GET, HEAD, or DELETE) causes schema rejection
- Providing incomplete or corrupted 402 challenge headers may yield an inconclusive verdict
- Network timeouts when the endpoint is unreachable

## How this service works

x402 Doctor: why a payment failed, in plain words: the cause, whose side it is on (your client, your wallet, the network, the seller or the facilitator) and how to fix it, from over 40 named causes (x402 and Coinbase facilitator codes, EVM and Solana, HTTP and network errors). Send the seller 402 as challenge and the error as response, by POST JSON or GET query. Unknown failures are reviewed nightly.

## Output

A JSON object with a 'verdict' field containing a plain-language classification of the failure (e.g. 'client_problem') indicating which party — client, wallet, network, or seller — is responsible for the payment failure, along with an explanation of what went wrong.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST",
      "PUT",
      "PATCH"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "verdict": "client_problem"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/maxwell-x402-payment-failure-diagnostics-80ce977b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.maxwellinternational.ai](https://www.zero.xyz/host/api.maxwellinternational.ai/llms.txt)