Skip to main content
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

Callback Request Format

After task completion, the system will send a POST request to your callBackUrl. The actual response structure in production looks like the following:
{
  "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

code
integer
required
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.
msg
string
required
Status message, usually "success". For detailed failure reasons, refer to data.errorMessage.
data.taskId
string
required
Task ID, consistent with the taskId returned when you submitted the task.
data.successFlag
integer
required
Generation status flag, with the same meaning as the Get Task Details endpoint:
ValueDescription
0GENERATING - Task is currently being processed
1SUCCESS - Image generated successfully; you can read response.resultImageUrl for the result
2CREATE_TASK_FAILED - Failed to create the task
3GENERATE_FAILED - Generation failed (for example flagged as sensitive content)
data.errorCode
integer
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)
data.errorMessage
string
Error message string, usually containing more detailed description for the failure.
data.response.resultImageUrl
string
Generated image URL on our server. Only present when successFlag = 1 and generation succeeds.
data.paramJson
string
JSON string snapshot of the request parameters for this task. Useful for debugging and auditing.
data.operationType
string
Internal model/config identifier, for example "nano-banana-2_1k".
data.createTime
string
Task creation time.
data.completeTime
string
Task completion time.

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');
});

Best Practices

Callback URL Configuration Recommendations

  1. Use HTTPS: Ensure callback URL uses HTTPS protocol for secure data transmission
  2. Verify Source: Verify the legitimacy of request sources in callback handling
  3. Idempotent Processing: The same taskId may receive multiple callbacks, ensure processing logic is idempotent
  4. Quick Response: Callback handling should return 200 status code quickly to avoid timeout
  5. Asynchronous Processing: Complex business logic should be processed asynchronously to avoid blocking callback response
  6. 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:
  • 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.