Copilot Agent Not Reading Attachments Sent via Direct Line API

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Posted on by AS-11030538-0

Hello Everyone,

I have been testing an approach to send prompts and attachments to an agent using REST APIs via Postman, and I wanted to share my observations to see if anyone else has experienced the same behavior.

We are sending JSON payloads that include the prompt along with attachment binaries (Base64 encoded). The API endpoint being used is:

https://directline.botframework.com/v3/directline/conversations

After testing multiple payload structures and scenarios, we noticed that the APIs work correctly when sending simple prompts. However, when attachments are included in the payload, the agent does not seem to process them correctly.

Scenarios tested and observed outcomes:

• Simple agent with one tool to retrieve an account record
Working as expected.

• Agent to read a document and update values in Dataverse
Returns a response stating that the attachment was not provided, even though the attachment is included in the payload.

• Agent to read a document without updating Dataverse
Returns generated/made-up values and presents them as if they were read from the document.

Additional observations:

• Attachments are passed in the payload as Base64-encoded content.
• The same behavior occurs when calling the API directly via Postman and when triggering the agent through Cloud Flow.
• The issue only appears when attachments are involved. Prompt-only scenarios work correctly.
• We also tried a few other payload structures and combinations, but they only work when attachments are not included in the request.

Has anyone successfully processed document attachments through the Direct Line API with an agent?
If there are any specific requirements, recommended payload formats, or configuration steps for handling attachments in document-processing scenarios, I would really appreciate any guidance.

Thank you!

Categories:

Copilot Studio pre-built agents/templates

Copilot Studio skills development

Autonomous agents

Building Copilot Studio chatbots in Microsoft Teams

Calling actions from Copilot Studio

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Nivedipa-MSFT Microsoft Employee on at

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Hello AS-11030538-0 - Base64-encoded attachments in the Direct Line JSON payload are not supported for agent document processing. The agent framework interprets the content field as structured content, such as Adaptive Cards, rather than binary file data. As a result, the agent may ignore the attachment or misinterpret its values.

How to Resolve

Option 1 — Use the multipart upload endpoint:

POST https://directline.botframework.com/v3/directline/conversations/{conversationId}/upload
Content-Type: multipart/form-data

Attach the file as a form part along with the activity JSON.

Option 2 — Use contentUrl instead of Base64:

{
"type": "message",
"from": { "id": "user1" },
"text": "Read this document",
"attachments": [{
    "contentType": "application/pdf",
    "contentUrl": "https://storage.blob.core.windows.net/docs/file.pdf",
    "name": "file.pdf"
}]
}

Store the file in Azure Blob Storage or SharePoint, and provide a publicly accessible or SAS-token URL.

For Cloud Flow: First upload the file to SharePoint or Blob Storage, then use the generated URL as the contentUrl in your Direct Line request.

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AS-11030538-0 14 on at

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Thanks for your reply.

I tried the approach you suggested, and it works well. The system is able to read the document from the URL and extract the required information.

However, we are now facing a different issue. After several attempts, we noticed that when we use document extraction together with the Dataverse tool to save the summary in Dataverse, we receive the following error:

Sorry, something unexpected happened. We’re looking into it.
Error code: SystemError
Conversation ID: C3nRnbJB0tGA3XkMCECVy4-in
Time (UTC): 3/13/2026 8:55:42 AM

We also tested a few other scenarios:

If we use the Dataverse tool without an attachment, it works correctly.

If we use the attachment without the tool, it also works fine.

The issue only occurs when we try to use both together.

Could you please confirm whether this combination is supported, or if there is any configuration we might be missing?

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Valantis 5,202 on at

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Hi@AS-11030538-0,

The file delivery is fine now (contentUrl/upload). The failure occurs when the agent passes the extracted content into the Dataverse step. Large or verbose payloads and longer-running flows commonly trigger a generic SystemError/timeout.

Keep the write payload small

Summarize/truncate the extracted text and pass only what you persist (e.g., title, key fields, short summary). Store the full document in SharePoint/Blob and save only the URL in Dataverse.

Write to Dataverse

If you use a Power Automate flow: make sure it returns within platform limits and only returns minimal outputs to the agent. Check the flow run history for failures/timeouts; fix and republish.

If you use a Dataverse connector step: pass only required columns and avoid large text blobs in a single turn.

Validate

Test with a tiny constant string (e.g., “hello”) into the Dataverse step after extraction. If it succeeds, gradually increase the summary length until you find a safe ceiling, then keep the summarizer below it.

Recheck connection references (Dataverse/Flow), re‑authenticate if prompted, republish the agent, and retry.

Quick checks

If you see SystemError again, reduce the text passed between actions or split the operation across turns (save URL + short summary now, add details later).

Always keep Direct Line activities small; use URLs/attachments for large content.

Best regards,

Valantis

✅ If this helped solve your issue, please Accept as Solution so others can find it quickly.

❤️ If it didn’t fully solve it but was still useful, please click “Yes” on “Was this reply helpful?” or leave a Like :).

🏷️ For follow-ups @Valantis.

📝 https://valantisond365.com/

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AS-11030538-0 14 on at

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Hi @Valantis

Thank you for the detailed suggestions.

Following your guidance, we performed additional testing today focusing specifically on the Direct Line API scenario using Postman.

To eliminate the possibility of large payloads causing the issue, we modified our setup for testing purposes:

In the Dataverse update tool, we hardcoded the Row ID of an existing record.

Instead of passing any dynamic content, we used a simple hardcoded string value ("Hello") for the field being updated.

The goal was to verify whether the Dataverse update step would succeed when the payload size is minimal.

Test Flow
The request was executed through Direct Line API via Postman using the following flow:

Send a message to the agent via Direct Line with a PDF attachment using contentUrl

The agent processes the attachment

The agent then executes the Dataverse update tool

The Dataverse update uses:

Hardcoded Row ID

Hardcoded value ("Hello")

This ensures that no dynamic content is passed to Dataverse, keeping the payload extremely small.

Result
Despite using a minimal payload, the request still fails when both steps occur in the same execution.
The Direct Line response returns the following error:

Sorry, something unexpected happened. We’re looking into it.
Error code: SystemError
The trace activity returned by Direct Line also shows:
"valueType": "ErrorCode",
"value": {
"ErrorCode": "SystemError"
}

Observation
From today's testing through Direct Line API, we observed:

Attachment processing works correctly

Dataverse tool execution works correctly when tested independently

However, when attachment processing and Dataverse execution are triggered together in the same Direct Line interaction, the request fails with SystemError

Since the Dataverse payload in this test was only a small constant string, it appears the issue may not be related to payload size.
Could you please confirm whether there are any known limitations or configuration requirements when combining attachment processing with Dataverse operations in the same Direct Line request?

Thank you again for your guidance.

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Valantis 5,202 on at

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Hi @AS-11030538-0,

Thanks for testing.

Based on the latest results, this does not look like a payload-size issue anymore. Since the attachment is processed correctly on its own, and the Dataverse update also works correctly on its own, the failure seems to happen specifically when both are executed together in the same Direct Line interaction.

From the Microsoft documentation I could find, I’m not able to confirm a supported pattern where a Copilot Studio agent processes an uploaded attachment and then performs a Dataverse update in the same Direct Line turn.

Microsoft documents file handling by capturing the attachment from System.Activity.Attachments and passing it into a flow/tool, which suggests the safer design is to handle the file processing and Dataverse update inside that flow/tool, then return only a small success/failure result back to the agent.

There is also a current Microsoft-documented limitation around attachments in Copilot Studio channels, including Direct Line, unless the message is sent to a supported skill. Because of that, this may be a channel/orchestration limitation rather than a configuration issue in your payload.

My recommendation is:

keep the current attachment upload approach

move the document processing + Dataverse update into the flow/tool itself

return only a minimal response to the agent

if this same pattern is required in a single Direct Line interaction, raise a Microsoft support case with the repro details and trace IDs, as this now looks more like a platform limitation than a payload problem

here also few links to check if you havent already:

Error codes and size limits

Quotas and limits for Copilot Studio

Testing and orchestration guidance

Best regards,

Valantis

✅ If this helped solve your issue, please Accept as Solution so others can find it quickly.

❤️ If it didn’t fully solve it but was still useful, please click “Yes” on “Was this reply helpful?” or leave a Like :).

🏷️ For follow-ups @Valantis.

📝 https://valantisond365.com/

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