curl --request POST \
--url https://api.sandbox.brickken.com/x402/agent/feedback/respond \
--header 'Content-Type: application/json' \
--header 'X-Payment: <api-key>' \
--data '
{
"chainId": "8453",
"agentId": "<string>",
"clientAddress": "<string>",
"feedbackIndex": "<string>",
"responseURI": "<string>",
"executionMode": "client-signed",
"signerAddress": "<string>",
"gasLimit": "<string>",
"nonce": 123,
"privateRpcUrl": "<string>",
"ownerEmail": "jsmith@example.com",
"email": "jsmith@example.com",
"responseHash": "<string>"
}
'import requests
url = "https://api.sandbox.brickken.com/x402/agent/feedback/respond"
payload = {
"chainId": "8453",
"agentId": "<string>",
"clientAddress": "<string>",
"feedbackIndex": "<string>",
"responseURI": "<string>",
"executionMode": "client-signed",
"signerAddress": "<string>",
"gasLimit": "<string>",
"nonce": 123,
"privateRpcUrl": "<string>",
"ownerEmail": "jsmith@example.com",
"email": "jsmith@example.com",
"responseHash": "<string>"
}
headers = {
"X-Payment": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {'X-Payment': '<api-key>', 'Content-Type': 'application/json'},
body: JSON.stringify({
chainId: '8453',
agentId: '<string>',
clientAddress: '<string>',
feedbackIndex: '<string>',
responseURI: '<string>',
executionMode: 'client-signed',
signerAddress: '<string>',
gasLimit: '<string>',
nonce: 123,
privateRpcUrl: '<string>',
ownerEmail: 'jsmith@example.com',
email: 'jsmith@example.com',
responseHash: '<string>'
})
};
fetch('https://api.sandbox.brickken.com/x402/agent/feedback/respond', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.sandbox.brickken.com/x402/agent/feedback/respond",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'chainId' => '8453',
'agentId' => '<string>',
'clientAddress' => '<string>',
'feedbackIndex' => '<string>',
'responseURI' => '<string>',
'executionMode' => 'client-signed',
'signerAddress' => '<string>',
'gasLimit' => '<string>',
'nonce' => 123,
'privateRpcUrl' => '<string>',
'ownerEmail' => 'jsmith@example.com',
'email' => 'jsmith@example.com',
'responseHash' => '<string>'
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-Payment: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.sandbox.brickken.com/x402/agent/feedback/respond"
payload := strings.NewReader("{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-Payment", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.sandbox.brickken.com/x402/agent/feedback/respond")
.header("X-Payment", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.sandbox.brickken.com/x402/agent/feedback/respond")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-Payment"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}"
response = http.request(request)
puts response.read_body{
"transactions": {},
"txId": "<string>",
"info": {}
}Respond to Feedback
Prepare an ERC-8004 feedback response through x402.
curl --request POST \
--url https://api.sandbox.brickken.com/x402/agent/feedback/respond \
--header 'Content-Type: application/json' \
--header 'X-Payment: <api-key>' \
--data '
{
"chainId": "8453",
"agentId": "<string>",
"clientAddress": "<string>",
"feedbackIndex": "<string>",
"responseURI": "<string>",
"executionMode": "client-signed",
"signerAddress": "<string>",
"gasLimit": "<string>",
"nonce": 123,
"privateRpcUrl": "<string>",
"ownerEmail": "jsmith@example.com",
"email": "jsmith@example.com",
"responseHash": "<string>"
}
'import requests
url = "https://api.sandbox.brickken.com/x402/agent/feedback/respond"
payload = {
"chainId": "8453",
"agentId": "<string>",
"clientAddress": "<string>",
"feedbackIndex": "<string>",
"responseURI": "<string>",
"executionMode": "client-signed",
"signerAddress": "<string>",
"gasLimit": "<string>",
"nonce": 123,
"privateRpcUrl": "<string>",
"ownerEmail": "jsmith@example.com",
"email": "jsmith@example.com",
"responseHash": "<string>"
}
headers = {
"X-Payment": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {'X-Payment': '<api-key>', 'Content-Type': 'application/json'},
body: JSON.stringify({
chainId: '8453',
agentId: '<string>',
clientAddress: '<string>',
feedbackIndex: '<string>',
responseURI: '<string>',
executionMode: 'client-signed',
signerAddress: '<string>',
gasLimit: '<string>',
nonce: 123,
privateRpcUrl: '<string>',
ownerEmail: 'jsmith@example.com',
email: 'jsmith@example.com',
responseHash: '<string>'
})
};
fetch('https://api.sandbox.brickken.com/x402/agent/feedback/respond', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.sandbox.brickken.com/x402/agent/feedback/respond",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'chainId' => '8453',
'agentId' => '<string>',
'clientAddress' => '<string>',
'feedbackIndex' => '<string>',
'responseURI' => '<string>',
'executionMode' => 'client-signed',
'signerAddress' => '<string>',
'gasLimit' => '<string>',
'nonce' => 123,
'privateRpcUrl' => '<string>',
'ownerEmail' => 'jsmith@example.com',
'email' => 'jsmith@example.com',
'responseHash' => '<string>'
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-Payment: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.sandbox.brickken.com/x402/agent/feedback/respond"
payload := strings.NewReader("{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-Payment", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.sandbox.brickken.com/x402/agent/feedback/respond")
.header("X-Payment", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.sandbox.brickken.com/x402/agent/feedback/respond")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-Payment"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"chainId\": \"8453\",\n \"agentId\": \"<string>\",\n \"clientAddress\": \"<string>\",\n \"feedbackIndex\": \"<string>\",\n \"responseURI\": \"<string>\",\n \"executionMode\": \"client-signed\",\n \"signerAddress\": \"<string>\",\n \"gasLimit\": \"<string>\",\n \"nonce\": 123,\n \"privateRpcUrl\": \"<string>\",\n \"ownerEmail\": \"jsmith@example.com\",\n \"email\": \"jsmith@example.com\",\n \"responseHash\": \"<string>\"\n}"
response = http.request(request)
puts response.read_body{
"transactions": {},
"txId": "<string>",
"info": {}
}agentAppendFeedbackResponse.
Authentication
Preparing charges the first half of the operation price, andPOST /send-transactions charges the rest. Each paid call answers 402 Payment Required with a PAYMENT-REQUIRED header describing the chain, asset, transfer method, amount, recipient, and timeout. Sign each payment locally and retry with X-PAYMENT.
A valid x-api-key is accepted instead of paying, on both steps.
See Authentication for the full credential matrix.
Key Fields
| Parameter | Required | Description |
|---|---|---|
chainId | Yes | Target chain ID. Use 8453 for Base mainnet or 84532 for Base Sepolia. Decimal and hex values are accepted. |
executionMode | No | client-signed (default) or client-broadcast. |
signerAddress | Yes | Wallet that signs the prepared transaction. |
agentId | Yes | On-chain agent ID. |
clientAddress | Yes | Client wallet associated with the feedback. |
feedbackIndex | Yes | Feedback entry index. |
responseURI | Yes | Off-chain response URI. |
responseHash | No | Optional hash for the response content. |
Response
Returns prepared unsigned transactions andtxId. Sign the transaction locally and submit it to POST /send-transactions as { txId, signedTransactions }.
Next step
Preparing does not touch the chain. The response gives youtxId, the unsigned transactions, and an x402Requirements quote.
Choose who broadcasts
client-signed (the default) — you sign the transaction and Brickken broadcasts it. client-broadcast — you sign and broadcast it yourself, then confirm with txHash. Either way the operation price is split evenly: half at prepare, half at send.Submit it and settle the payment
POST to /send-transactions. The first attempt answers 402 Payment Required; read PAYMENT-REQUIRED, sign the payment locally, and retry with X-PAYMENT. An x-api-key is accepted here instead of paying.Poll until it confirms
GET /get-transaction-status with the txId. Your payment settles only after the operation confirms, and is released if it reverts.Authorizations
Base64-encoded x402 payment payload. Supported for x402-eligible agentic methods on /x402/... facades, /prepare-transactions, and eligible /send-transactions retries.
Body
Target operation chain ID. Use 8453 on Base mainnet or 84532 on Base Sepolia.
"8453"
"84532"
Original feedback client address.
^0x[a-fA-F0-9]{40}$Feedback index to respond to.
Execution mode. Use brickken-relayed to let Brickken's relayer sign, pay gas, and broadcast (omit signerAddress). Use client-signed to sign the prepared transaction yourself.
brickken-relayed, client-signed Wallet that signs the prepared blockchain transaction. Required only in client-signed mode; omit in brickken-relayed mode.
^0x[a-fA-F0-9]{40}$Optional explicit gas limit.
Optional explicit nonce when managing nonces manually.
Optional private RPC URL override.
Optional owner attribution email.
Alias for ownerEmail where supported.