When you submit image generation tasks to the NanoBanana Generate-2 API (/api/v1/nanobanana/generate-2), you can set a callback address through the callBackUrl parameter. After the task is completed, the system will automatically push the results to your specified address.
Callback Mechanism Overview
The callback mechanism eliminates the need for you to poll the API to query task status. The system will actively push task completion results to your server.
Callback Timing
The system will send callback notifications in the following situations:
NanoBanana Generate-2 image generation task completed successfully
NanoBanana Generate-2 image generation task failed
Error occurred during task processing
Callback Method
HTTP Method : POST
Content Type : application/json
Timeout Setting : 15 seconds
After task completion, the system will send a POST request to your callBackUrl. The actual response structure in production looks like the following:
Success Callback Example
Sensitive Content Failure Callback Example
{
"code" : 200 ,
"msg" : "success" ,
"data" : {
"taskId" : "31ce2c17b257492959d62279e6d01a54" ,
"paramJson" : "{...}" ,
"completeTime" : "2026-02-27 24:00:00" ,
"response" : {
"originImageUrl" : null ,
"resultImageUrl" : "https://tempfile.aiquickdraw.com/gemini-preview/xxxxxx.jpeg"
},
"successFlag" : 1 ,
"errorCode" : null ,
"errorMessage" : null ,
"operationType" : "nano-banana-2_1k" ,
"createTime" : "2026-02-27 24:00:00"
}
}
Field and Status Description
Top-level code field indicating whether the callback request itself is successful.
In the current implementation it is typically 200 for normal callbacks.
Whether the generation task is successful should be determined by data.successFlag and data.errorCode.
Status message, usually "success". For detailed failure reasons, refer to data.errorMessage.
Task ID, consistent with the taskId returned when you submitted the task.
Generation status flag, with the same meaning as the Get Task Details endpoint: Value Description 0 GENERATING - Task is currently being processed 1 SUCCESS - Image generated successfully; you can read response.resultImageUrl for the result 2 CREATE_TASK_FAILED - Failed to create the task 3 GENERATE_FAILED - Generation failed (for example flagged as sensitive content)
Error code when successFlag ≠ 1, indicating the failure reason, for example:
422: The input or output was flagged as sensitive content (see the sensitive content failure example above)
Error message string, usually containing more detailed description for the failure.
data.response.resultImageUrl
Generated image URL on our server. Only present when successFlag = 1 and generation succeeds.
JSON string snapshot of the request parameters for this task. Useful for debugging and auditing.
Internal model/config identifier, for example "nano-banana-2_1k".
Callback Reception Examples
Here are example codes for receiving NanoBanana Generate-2 callbacks in popular programming languages:
const express = require ( 'express' );
const fs = require ( 'fs' );
const https = require ( 'https' );
const app = express ();
app . use ( express . json ());
app . post ( '/nanobanana-generate-2-callback' , ( req , res ) => {
const { code , msg , data } = req . body ;
const {
taskId ,
successFlag ,
errorCode ,
errorMessage ,
response
} = data || {};
const resultImageUrl = response ?. resultImageUrl || '' ;
console . log ( 'Received NanoBanana Generate-2 callback:' , {
taskId ,
httpCode: code ,
successFlag ,
errorCode ,
message: msg ,
errorMessage
});
if ( successFlag === 1 ) {
// Task completed successfully
console . log ( 'NanoBanana Generate-2 task completed successfully' );
console . log ( `Generated image URL: ${ resultImageUrl } ` );
// Download the generated image
if ( resultImageUrl ) {
downloadFile ( resultImageUrl , `nanobanana_generate2_result_ ${ taskId } .jpg` )
. then (() => console . log ( 'Generated image downloaded successfully' ))
. catch ( err => console . error ( 'Failed to download generated image:' , err ));
}
} else {
// Task failed
console . log ( 'NanoBanana Generate-2 task failed:' , errorMessage || msg || 'Unknown error' );
if ( errorCode === 422 ) {
console . log ( 'Content/safety checks failed - please adjust your prompt or inputs' );
}
}
// Return 200 status code to confirm callback receipt
res . status ( 200 ). json ({ status: 'received' });
});
// Helper function: download file
function downloadFile ( url , filename ) {
return new Promise (( resolve , reject ) => {
const file = fs . createWriteStream ( filename );
https . get ( url , ( response ) => {
if ( response . statusCode === 200 ) {
response . pipe ( file );
file . on ( 'finish' , () => {
file . close ();
resolve ();
});
} else {
reject ( new Error ( `HTTP ${ response . statusCode } ` ));
}
}). on ( 'error' , reject );
});
}
app . listen ( 3000 , () => {
console . log ( 'NanoBanana Generate-2 callback server running on port 3000' );
});
from flask import Flask, request, jsonify
import requests
import os
app = Flask( __name__ )
@app.route ( '/nanobanana-generate-2-callback' , methods = [ 'POST' ])
def handle_callback ():
data = request.json
code = data.get( 'code' )
msg = data.get( 'msg' )
callback_data = data.get( 'data' , {})
task_id = callback_data.get( 'taskId' )
success_flag = callback_data.get( 'successFlag' )
error_code = callback_data.get( 'errorCode' )
error_message = callback_data.get( 'errorMessage' )
response_data = callback_data.get( 'response' ) or {}
result_image_url = response_data.get( 'resultImageUrl' )
print ( "Received NanoBanana Generate-2 callback:" )
print ( f "Task ID: { task_id } " )
print ( f "HTTP code: { code } , successFlag: { success_flag } , errorCode: { error_code } " )
print ( f "msg: { msg } , errorMessage: { error_message } " )
if success_flag == 1 :
# Task completed successfully
print ( "NanoBanana Generate-2 task completed successfully" )
print ( f "Generated image URL: { result_image_url } " )
# Download the generated image
if result_image_url:
try :
result_filename = f "nanobanana_generate2_result_ { task_id } .jpg"
download_file(result_image_url, result_filename)
print ( f "Generated image downloaded as { result_filename } " )
except Exception as e:
print ( f "Failed to download generated image: { e } " )
else :
# Task failed
print ( f "NanoBanana Generate-2 task failed: { error_message or msg } " )
if error_code == 422 :
print ( "Content/safety checks failed - please adjust your prompt or inputs" )
# Return 200 status code to confirm callback receipt
return jsonify({ 'status' : 'received' }), 200
def download_file ( url , filename ):
"""Download file from URL and save locally"""
response = requests.get(url, stream = True )
response.raise_for_status()
os.makedirs( 'downloads' , exist_ok = True )
filepath = os.path.join( 'downloads' , filename)
with open (filepath, 'wb' ) as f:
for chunk in response.iter_content( chunk_size = 8192 ):
f.write(chunk)
if __name__ == '__main__' :
app.run( host = '0.0.0.0' , port = 3000 )
<? php
header ( 'Content-Type: application/json' );
// Get POST data
$input = file_get_contents ( 'php://input' );
$data = json_decode ( $input , true );
$code = $data [ 'code' ] ?? null ;
$msg = $data [ 'msg' ] ?? '' ;
$callbackData = $data [ 'data' ] ?? [];
$taskId = $callbackData [ 'taskId' ] ?? '' ;
$successFlag = $callbackData [ 'successFlag' ] ?? null ;
$errorCode = $callbackData [ 'errorCode' ] ?? null ;
$errorMessage = $callbackData [ 'errorMessage' ] ?? '' ;
$response = $callbackData [ 'response' ] ?? [];
$resultImageUrl = $response [ 'resultImageUrl' ] ?? '' ;
error_log ( "Received NanoBanana Generate-2 callback:" );
error_log ( "Task ID: $taskId " );
error_log ( "HTTP code: $code , successFlag: $successFlag , errorCode: $errorCode " );
error_log ( "msg: $msg , errorMessage: $errorMessage " );
if ( $successFlag === 1 ) {
// Task completed successfully
error_log ( "NanoBanana Generate-2 task completed successfully" );
error_log ( "Generated image URL: $resultImageUrl " );
// Download the generated image
if ( ! empty ( $resultImageUrl )) {
try {
$resultFilename = "nanobanana_generate2_result_{ $taskId }.jpg" ;
downloadFile ( $resultImageUrl , $resultFilename );
error_log ( "Generated image downloaded as $resultFilename " );
} catch ( Exception $e ) {
error_log ( "Failed to download generated image: " . $e -> getMessage ());
}
}
} else {
// Task failed
error_log ( "NanoBanana Generate-2 task failed: " . ( $errorMessage ?: $msg ));
if ( $errorCode === 422 ) {
error_log ( "Content/safety checks failed - please adjust your prompt or inputs" );
}
}
// Return 200 status code to confirm callback receipt
http_response_code ( 200 );
echo json_encode ([ 'status' => 'received' ]);
function downloadFile ( $url , $filename ) {
$downloadDir = 'downloads' ;
if ( ! is_dir ( $downloadDir )) {
mkdir ( $downloadDir , 0755 , true );
}
$filepath = $downloadDir . '/' . $filename ;
$fileContent = file_get_contents ( $url );
if ( $fileContent === false ) {
throw new Exception ( "Failed to download file from URL" );
}
$result = file_put_contents ( $filepath , $fileContent );
if ( $result === false ) {
throw new Exception ( "Failed to save file locally" );
}
}
?>
Best Practices
Callback URL Configuration Recommendations
Use HTTPS : Ensure callback URL uses HTTPS protocol for secure data transmission
Verify Source : Verify the legitimacy of request sources in callback handling
Idempotent Processing : The same taskId may receive multiple callbacks, ensure processing logic is idempotent
Quick Response : Callback handling should return 200 status code quickly to avoid timeout
Asynchronous Processing : Complex business logic should be processed asynchronously to avoid blocking callback response
Timely Download : Download image files promptly after receiving successful callbacks
Important Reminders
Callback URL must be a publicly accessible address
Server must respond within 15 seconds, otherwise it will be considered timeout
After 3 consecutive retry failures, the system will stop sending callbacks
Ensure stability of callback handling logic to avoid callback failures due to exceptions
Parse data.info.resultImageUrl field properly to get the generated image URL
Need to handle multiple error status codes (400, 500, 501), implement complete error handling
Handle both success and failure scenarios appropriately
Troubleshooting
If you haven’t received callback notifications, please check the following:
Network Connection Issues
Confirm callback URL is accessible from the public internet
Check firewall settings to ensure inbound requests are not blocked
Verify domain name resolution is correct
Ensure server returns HTTP 200 status code within 15 seconds
Check server logs for error information
Verify interface path and HTTP method are correct
Confirm received POST request body is in JSON format
Check if Content-Type is application/json
Verify JSON parsing is correct
Confirm image URL is accessible
Check image download permissions and network connection
Verify image save path and permissions
Implement reasonable image download and storage logic
Review content policy violation prompts in error messages
Adjust flagged prompt content
Ensure prompts comply with platform content guidelines
Check for sensitive or inappropriate content
Check if generation parameters are reasonable
Verify input image format and quality (for auto aspect ratio)
Confirm prompt length and format
Consider adjusting generation parameters and retry
Alternative Solution
If you cannot use the callback mechanism, you can also use polling:
Polling Query Results Use the get task details interface to periodically query task status, recommended every 30 seconds.