Copilot Studio (New Agent Experience) – File input not passed to flow tool (contentBytes empty)

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Posted on by BD-02060115-0

Hi all,

I’m testing the new Copilot Studio agent experience (June 2026) and ran into an issue when using a Power Automate flow as a tool.

Scenario

Created a flow with trigger: “When an agent calls the workflow”

Added inputs:
- File (type: File)
- Text (type: string)

Added the flow as a tool in the agent

Issue

When I configure the tool inside the agent:

✅ The Text input appears in the agent UI

❌ The File input does NOT appear at all

So I’m unable to:

Map the uploaded file to the flow input

Pass file content (contentBytes) into the flow

bserved behavior

Even though the flow clearly has a File input defined, the agent:
- Only shows text parameters
- Does not expose the File parameter for mapping

When the flow runs:
- File object is present but:
  bserved behavior
  - Even though the flow clearly has a File input defined, the agent:
    - Only shows text parameters
    - Does not expose the File parameter for mapping
  - When the flow runs:
    - File object is present but:

Screenshot 2026-0...

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sannavajjala87 457 Super User 2026 Season 1 on at

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Hi,

what you’re seeing is expected with the current Copilot Studio agent experience, when a Power Automate flow is exposed as a tool, the agent UI only surfaces primitive inputs like text, and File inputs are not exposed for mapping. Even if the flow defines a File parameter, the agent doesn’t pass a true file payload; instead it sends a placeholder record, which is why the flow runs with "contentBytes": "". This is a known limitation where uploaded files are not automatically transferred as raw bytes to flows, and the { name, contentBytes } structure is just a schema rather than populated content. In practice, you’ll need to either capture the file inside a topic and explicitly construct the file object before calling the flow, or use a reference-based approach (e.g., store the file in SharePoint/Blob and pass the file URL or ID to the flow).

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André Arnaud de Cal... 679 on at

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Hi,

As a workaround, you can try to convert the file into Base64 and then pass it as text to your flow.

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Manoj - ManoVerse 28 on at

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Yes, this looks like a current limitation/behavior in the new Copilot Studio agent tool experience.Power Automate flow has a File input, Copilot Studio may not show it as a mappable parameter in the tool UI. best approach is to pass the uploaded file as separate values: contentBytes and name.
Use:
First(System.Activity.Attachments).Content for file content

and
First(System.Activity.Attachments).Name for file name.
If ContentBytes is still blank, make sure the file is collected using a File question and Include file metadata is enabled.
As a workaround as mentioned by Andre you can convert/pass the file content as Base64 text using a string input in the flow, then decode/use it inside Power Automate. This avoids depending on the File input mapping UI.

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