Why does the streamGenerateGroundedContent method return a 404 error in the Google Discovery Engine API?

Below is a summary of the likely causes and next steps to resolve the 404 “Method not found” error for streamGenerateGroundedContent.

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Why Might You Get a 404 for streamGenerateGroundedContent?

• Endpoint Availability:
  Although the nonstreaming endpoint (GenerateGroundedContent) works, the streaming version (streamGenerateGroundedContent) is provided as a preview or experimental feature. In many cases, experimental methods may not be generally available for every project or region. A 404 “Method not found” error is typically returned when the service does not expose the requested RPC.

• Project/Region Settings:
  Even though Vertex AI and Discovery Engine are enabled, some endpoints may require additional rollout flags or be limited to a specific region. For example, if the method is only available in certain regions (or with specific project configurations), calling it using the global endpoint can yield a 404.

• API Version:
  Ensure that you are using the correct API version in your URL. The streaming endpoint is documented under v1beta. A typo or incorrect version might lead to attempting to access a nonexistent endpoint.

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What to Do Next

1. Verify the Feature’s Availability:
   Double-check the documentation to see if streaming generation is limited to a set of beta testers or if there are special instructions for enabling the feature. Often Google releases streaming endpoints in phases.

2. Check the Endpoint URL and API Version:
   Make sure that the URL exactly matches what is prescribed in the documentation. For instance, confirm that your project number, region, and API version are correct. For example, if the documentation states:

   BASHCopied
   https://discoveryengine.googleapis.com/v1beta/projects/your-project-number/locations/global:streamGenerateGroundedContent

   then ensure there are no typographical errors.

3. Region or Service Account Requirements:
   Look into whether any additional settings (such as enabling the full suite of permissions in a particular region or updating your service account’s roles) are required.

4. Fallback to the Nonstreaming API:
   Since GenerateGroundedContent works, consider using that endpoint until confirmation is provided that streamGenerateGroundedContent is generally available for your project.

5. Contact Support or Consult Release Notes:
   If the above steps do not resolve the issue, consider checking the release notes or reaching out to Google Cloud support to confirm whether streaming generation is enabled for your project.

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Example of a Correct cURL Command

Here is an example based on the instructions in case you’d like to double-check against your command:

BASHCopied
curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  -H "Content-Type: application/json" \
  "https://discoveryengine.googleapis.com/v1beta/projects/my-project-number/locations/global:streamGenerateGroundedContent" \
  -d '[
  {
    "contents": [
      {
        "role": "user",
        "parts": [
          {
            "text": "Summarize How to delete a data store in Vertex AI Agent Builder?"
          }
        ]
      }
    ],
    "groundingSpec": {
      "groundingSources": [
        {
          "googleSearchSource": {}
        }
      ]
    },
    "generationSpec": {
      "modelId": "gemini-1.5-flash"
    }
  }
]'

Double-check that your project number is correct and that all parameters match the documentation.

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Conclusion

The 404 error indicates that the streaming method isn’t found in your current configuration. This is most likely due to the endpoint being experimental or regionally limited. Verify the availability of the streaming endpoint per the latest documentation and consider using the nonstreaming version if immediate testing is needed.