[400 Bad Request] Request has empty input. with subagent

Questions
1

Hello !
I’m a beginner and i’m start to discover N8N. As many, I try to create an assistant and test some functions with different services.
Currently, I try to make my agent work with Outlook calendar through Telegram chat, and I’ve now a strange message, knowing that it was working fine few days ago…

Describe the problem/error/question

I’ve a main agent and a sub agent which is dedicated to calendar.
When I request something (list events, etc.), I receive an error from the sub agent saying :
[GoogleGenerativeAI Error]: Error fetching from https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent: [400 Bad Request] Request has empty input.

What is the error message (if any)?

[GoogleGenerativeAI Error]: Error fetching from https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent: [400 Bad Request] Request has empty input.

Please share your workflow

Share the output returned by the last node

No parameters are set up to be filled by AI. Click on the :sparkles: button next to a parameter to allow AI to set its value.

Bad request - please check your parameters
[GoogleGenerativeAI Error]: Error fetching from https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent: [400 Bad Request] Request has empty input.

Information on your n8n setup

  • n8n version: 1.120.3
  • Database (default: SQLite):
  • n8n EXECUTIONS_PROCESS setting (default: own, main):
  • Running n8n via (Docker, npm, n8n cloud, desktop app): Docker
  • Operating system:

Do you have an idea about the issue and the root cause ?
If I define the tool directly, without a sub agent, there is no issue.

Thank you !

2

The “Request has empty input” error with Google Gemini usually means the AI node isn’t receiving any input text to process. Here are the most common fixes:

• Check that your sub-agent is properly receiving input from the main agent - verify the connection between agents and ensure data is being passed correctly

• In your Gemini AI node, make sure the “Message” field contains actual content (like `{{ $json.input }}` or the appropriate expression)

• Test your sub-agent independently by manually providing input to see if it works in isolation

• Check if there are any empty variables or expressions in your prompt that might be causing the input to be blank

Since it was working before, something likely changed in how the input is being passed between your main agent and calendar sub-agent.