MCP client with Google Vertex Chat

Questions
1

Hi All,

I am using n8n.io hosted version 1.93.0. I have a very basic workflow where I am using Google Vertex Chat node and an MCP client tool connected to an AI Assistant root node. I have verified that the n8n.io platform can reach my MCP server, and that all tools from that MCP server are found.

The issue appears to be when n8n feeds that tool information to Google Vertex Chat. See error below.

Any thoughts / suggestions?

Bad request - please check your parameters

Invalid JSON payload received. Unknown name “type” at ‘tools[0].function_declarations[0].parameters.properties[0].value’: Proto field is not repeating, cannot start list. Invalid JSON payload received. Unknown name “type” at ‘tools[0].function_declarations[0].parameters.properties[1].value’: Proto field is not repeating, cannot start list.
}

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image2863×1034 274 KB

2

Hello, @Jeremy_Schulman!

That actually happened to me before.

Check if, inside your MCP workflow, you have any nodes with special characters in their names — like dots (.), commas (,), or others. Those can cause issues during the connection or execution.

Try renaming those nodes to use only letters, numbers, and underscores — and see if that resolves it.

Let me know if that helps!

3

Hi @joao_antunes - thank you for your reply! Good to hear that I am not the only one that has experienced this.

I am brand new to using N8N. I have my MCP client (NetBox MCP), but the tool names are formed with only lower-case letters and underscores. For example “netbox_find_all_circuits”.

It was not clear to me what you meant by “renaming those nodes”; if you were referring to the MCP tools names or something else.

Thank you again!

4

Can you show you MCP workflow, please?

5

Hi @joao_antunes - When you say “MCP workflow”, I am not certain what this. I have an MCP client node that is communicating with my MCP server (outside of n8n). I have an AI assistant node that connects my Google Vertex AI Model node and the MCP client node. Sorry to not completely understand as I am still learning. Really appreciate your help.

6

Understood! Then I don’t know how to help you further, sorry!

7

I appreciate you trying. I am certain I will get more information and will update this thread when I know more.

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