Trouble with Vertex AI (Gemini) Streaming Response in callin.io Self-Hosted Workflows

Hello callin.io Community,

I’m currently implementing a high-level smart automation solution called NextGen Varejo: Control and Intelligence, designed for Brazilian retailers like supermarkets and pharmacies. The platform integrates directly with the ERP system and is powered by multiple specialized AI Agents (Inventory, Finance, Marketing, Customer, Social Media), all orchestrated by a central module called the MCP – Model Context Protocol.

At the heart of the AI engine, we use Vertex AI (Gemini) from Google Cloud for natural language understanding and generation, embedded directly into “Entry Agents” – smart gateways that route contextual requests to the appropriate AI agents. All of this is visually orchestrated in callin.io self-hosted (v1.101.2).

The Problem

When using the Google Gemini and AI Agent nodes from the @n8n/n8n-nodes-langchain package, we encounter this error:

"Cannot read properties of undefined (reading 'Symbol(Symbol.asyncIterator)')"

This happens when the Gemini model attempts to return a streaming response using the streamGenerateContent method – which appears to be improperly handled by the current version of the node.

What We’ve Verified

• Authentication with Vertex AI via Service Account is fully working;
• The Gemini model is active in the us-central1 region;
• The Google API is being called successfully (this is not a Google Cloud error);
• The correct endpoint (generateContent or streamGenerateContent) is being used;
• The error occurs only when the callin.io node tries to process the streaming response.

Workarounds in Progress

• We’re building a dedicated sub-workflow using the HTTP Request node, manually calling the Gemini REST API as a fallback;
• This sub-workflow will be connected via Execute Workflow to various AI Agents, until the native node handles streaming properly.

Why This Matters

This is part of a live retail automation system aimed at optimizing stock, marketing, communication and pricing decisions. Vertex AI is essential to generate real-time insights, customer content and campaign ideas. For this to work in production, reliable streaming response support is crucial.

If anyone in the community has experienced this issue or found a more efficient workaround (without losing the benefits of streaming), your help would be greatly appreciated!

Thanks in advance to the amazing callin.io community – your platform is incredibly powerful when paired with Google Cloud.

Best regards,
Elton Nunes dos Santos
NextGen Varejo | Belo Horizonte, Brazil
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