Pabbly MCP - OpenAI agent builder [500 errors from OpenAI Agent Builder when invoking Pabbly MCP custom API/webhook tools]

[FabeeoBreen]

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https://connect.pabbly.com/workflow/mapping/IjU3NjYwNTY0MDYzNjA0MzI1MjY5NTUzNjUxM2Ii_pc

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Hello Pabbly!
I’ve been testing the new OpenAI Agent Builder with Pabbly MCP. The connection works well and I can see the MCP tools I created in Pabbly. Managing Google Sheets works fine, but when I run a custom API call or use MCP to send data to another webhook, I consistently get a 500 error.
What’s odd is the request does go through—the destination webhook receives the data—yet the OpenAI agent still returns a 500.
Here’s a screen recording: https://gyazo.com/03a0f19ee8d83bec304de0ccf83d78e2
Am i doing something wrong?
Thank you!

 

[Preeti Paryani]

Hello @FabeeoBreen,

Thank you for sharing the details. Upon checking the workflow URL you provided, it seems that the trigger doesn’t contain any application. This is likely the reason you are encountering the 500 error, even though the destination webhook is receiving the data.

Please add the appropriate trigger application to your workflow and test again. This should resolve the issue

 

[FabeeoBreen]

Hey @Preeti Paryani !
Thanks for your reply!
Actually the workflow with the goggle sheet MCP is working fine without 500 error (even if it has not a trigger step)
workflow url: https://connect.pabbly.com/workflow/mapping/IjU3NjYwNTY0MDYzNjA0MzI1MjZmNTUzZDUxMzAi_pc
- When i exectute MCP command from openai agent, the Google operators runs fine and i can even see this happening in the Task History panel (see image) - I also get a success response from my agent.
BUT
- When i use the MCP to control a "Data forward" operator or "api call" operator i always get 500, even tho the data pass through, this never shows in the Task History panel.
Looks like the google operators are well configured and responding. - While the other operators gets the data but the MCP doesnt really trigger the workflow the same way it does with google operators.

 

[ArshilAhmad]

The MCP server is used to directly interact with the supported action steps in your workflow which is why you were able to execute Google Sheets action step in this workflow.

Pabbly

connect.pabbly.com

You won’t be able to send data to a webhook and trigger the workflow through it. Also, the Data Forwarder doesn’t support the MCP tool, so you won’t be able to execute it directly either. These are the only two steps you have in this workflow.

Pabbly

connect.pabbly.com