Custom Prompt

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Posted on by Matheus Oliveira

Hello all!

I've been working on this agent which is responsible to select a screw based on user inputs. It's expected to have a list of screws as output.

When I test the custom prompt (in "view model details" tab) it works very well, but when I test the whole topic it doesn't and I get this error message:

Error Message: The parameter with name 'predictionOutput' on prompt 'Custom prompt 12/01/2025, 04:45:36 PM' ('48326270-b444-469c-91cc-84c1246c97c7') evaluated to type 'RecordDataType' , expected type 'RecordDataType' Error Code: AIModelActionBadRequest Conversation Id: 56c59c05-1e03-4336-8e22-dfc82490d110 Time (UTC): 2026-03-05T18:29:35.759Z

Below you'll find my custom prompt.

Could anyone help me please?

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Topic creation & management

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MichaelFP 2,001 Moderator on at

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Did you request to your answer be a json on the prompt?

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Kalathiya 2,456 Super User 2026 Season 1 on at

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Hello @MO-10121135-0,

If possible, could you please paste the custom prompt here so we can review it? That will help us better understand what might be causing the issue.

The error message you shared usually happens when:

#1. Check output types – Make sure the prompt output matches the expected variable type.
#2. Check inputs – Verify all required inputs are connected to variables with values.
#3. Check for blank values – Ensure no required variable is blank before calling the prompt.
#4. Data Type Mismatch

Reference link:

https://learn.microsoft.com/en-us/troubleshoot/power-platform/copilot-studio/authoring/error-codes?tabs=webApp#aimodelactionbadrequest

If this response resolves your issue, please mark it as the Verified Answer so it can help other community members as well.

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Matheus Oliveira 6 on at

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Hello @Kalathiya, below you'll find my prompt:

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MichaelFP 2,001 Moderator on at

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@MO-10121135-0 as told early you must set the output type, your output is type text, you must set as json, so the data it will be parsed as object. On the right corner top of the prompt window you can changed that.

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Matheus Oliveira 6 on at

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Hello, @MichaelFP

I tried this even before my post, but without success. I've just tried it again, but it failed.

The truth is: I really don't know how to use JSON...

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MichaelFP 2,001 Moderator on at

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Check your prompt you do no tell to the LLM to generate as json you declare that you want to have the response as a JSON structure.
It is good to include a sample json to following the correct structure.

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Matheus Oliveira 6 on at

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Hello @MichaelFP,

I made this way and it ran into the same error. How could I improve that?

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MichaelFP 2,001 Moderator on at

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@Matheus Oliveira he created the list for you. But as I told for you before, you did not provide any example how do you want to have the output.

You need to say something like that:

"Set the output like an array with the all the values filtered. Example: { values: ['data 1','data 2','data 3']}"

You must set an example not leave for the Model to generate by it self.

In that case you will use result.structureOutput.values in the copilot studio.

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