Type Mismatch Error: 'StringDataType' expected 'FileDataType' in Copilot Studio (Flow Succeeded)

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Posted on by VS-26030531-0

Environment:

Platform: Microsoft Copilot Studio
Action: Power Automate Flow (Resume Builder Flow)
Trigger: "When Copilot Studio calls a flow"
Key Components: "Run a prompt" (AI Builder) within the flow.

The Issue:
I am experiencing a critical mismatch between Copilot Studio and Power Automate. When my agent triggers a flow to process a resume, the flow executes successfully in Power Automate (Status: Succeeded), but the Agent returns an error immediately.

The Error Message:

The parameter with name 'resume' on flow 'Resume Builder Flow' evaluated to type 'StringDataType', expected type 'FileDataType'. Error Code: FlowActionBadRequest.

Current Setup:

Question Node: Using File Entity with "Include metadata" enabled.
Power Fx Mapping: Passing the file to a flow input named Existing Resume using:
{ contentBytes: Topic.ResumeFile.Content, name: Topic.ResumeFile.Name }
Flow Trigger: The input Existing Resume is correctly set to the File type.
Flow Logic: I use a "Run a prompt" component. Inside this component, I pass Existing Resume.contentBytes into a prompt variable named resume.

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Connector development

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Sunil Kumar Pashikanti 1,994 Moderator on at

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Hi @VS-26030531-0,

Your flow actually succeeds, but Copilot Studio rejects the response before it can be consumed because of a type contract violation at the Copilot --> Flow boundary.

In short: Copilot Studio expects a FileDataType end‑to‑end, but your Power Automate flow (specifically the Run a prompt / AI Builder step) implicitly coerces the file input into a string, breaking the schema that Copilot Studio enforces. This is a known integration gap between Copilot Studio File entities and AI Builder prompts.

Why this happens

Copilot Studio File entities must remain FileDataType
Passing ExistingResume.contentBytes into Run a prompt converts it to StringDataType
Power Automate allows this internally --> Flow succeeds
Copilot Studio validates output schema strictly --> Agent fails immediately

Supported Fix
Do NOT pass contentBytes directly to “Run a prompt”.
Instead:

Pass the File object untouched into the flow
Use the file input directly inside AI Builder

Set the prompt variable type to File
Bind it to Existing Resume (not .contentBytes)

Let AI Builder handle file parsing internally

This preserves FileDataType and keeps Copilot Studio satisfied.

What will NOT work

Passing { contentBytes, name } manually
Mapping .contentBytes to prompt inputs
Using Compose between Copilot and Prompt
Returning strings when Copilot expects File

✅ If this answer helped resolve your issue, please mark it as Accepted so it can help others with the same problem.
👍 Feel free to Like the post if you found it useful.

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VS-26030531-0 4 on at

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@Sunil Kumar Pashikanti Thank you for your assistance.

I discovered that I had incorrectly configured the output parameter of the flow, but I have now resolved the issue.

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