Bug `TypeError: fetch failed` when using `generate_image` with gemini-3-pro-preview

[wunsir]

Description

I am encountering a persistent error when attempting to generate images using the Nano Banana MCP tool.
My Setup:

• I have access to the gemini-3-pro-preview model.
• I have installed the Nano Banana MCP tool.
• Authentication: I normally log in to the Gemini CLI using OAuth, but for this extension, I have specifically configured a separate API KEY.
• All necessary environment variables have been set up.
  The Issue:
  Despite the configuration looking correct, every time I run the image generation command, it fails with a fetch failed error.

Error Log

x  generate_image (nanobanana MCP Server) {"prompt": "a diagram"}                      
MCP tool 'generate_image' reported tool error for function call: {"name":"generate_image","args":{"prompt":"a diagram"}} with response:     
{"functionResponse":{"name":"generate_image","response":{"error":{"message":"MCP error -32603: An unexpected error occurred: exception      TypeError: fetch failed sending request","isError":true}}}}]   

I have asked gemini for help, but it does not work.
I would appreciate it if you could help me with this issue!

[caisah]

@wunsir Have you tried using a different prompt, more generic. I've been getting this error when the service cannot generate the image because of the image generation constraints.