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HTTP node in Copilot Studio Topic - 500 error with files in body (regression Jun 30)

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Posted on by MV-01071313-0

Hi everyone,
we are experiencing what looks like a platform-side regression in Copilot Studio and wanted to check if others are seeing the same behavior.

Setup: We implemented a declarative agent with a Topic that uses the native HTTP node (not a Power Automate flow) to call an Azure AI Foundry endpoint (Anthropic Messages API compatible, model claude-opus-4-6). We specifically chose the HTTP node inside the Topic because it allows configuring a custom timeout in milliseconds, which is not possible with agent flows.

What was working: The solution was tested and running solidly for approximately two days (June 26–29, 2026), including calls with PDF files passed as base64 in the request body.

What broke: Starting June 30, 2026, without any changes on our side, every HTTP call that includes a file of any kind in the body now returns 500 InternalServerError / HttpRequestFailure. This happens even with the exact same files and configuration that worked before.

Crucially, the same API endpoint works correctly when called from Python scripts and from Power Automate flows, so the issue is isolated to the native HTTP node inside a Copilot Studio Topic.

Conversation IDs for reference:
496519e9-13d0-497d-9457-990c9f5b5f0b – UTC: 2026-06-30T10:14:22.412Z

a:1FOfENJcd7PMuqwCzu3zUh5VDdqHdvaQZG5azYq_MHeQrq-V5ZNGK3H2cSmrwcXpmv2OrisNGsFPHmEk45-yk8SUIk9cWCRtXzQP8uM5fb2Q0Y1IxtmITQS2b9EX-28T6 – UTC: 2026-06-30T10:33:52.872Z

Has anyone else experienced this? Is there any known platform update or security blockers that could explain this behavior?
Thanks

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Prasad-MSFT Microsoft Employee on at

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Thanks for the detailed report and conversation IDs. We’re not currently aware of a confirmed platform-wide incident affecting Copilot Studio HTTP nodes, but your symptoms strongly suggest a possible change or regression in how the HTTP node handles file/base64 payloads.

Since the same endpoint works in Python and Power Automate but fails only in the Copilot Studio Topic HTTP node (starting June 30 with no config changes), this likely points to a runtime-level change such as stricter payload limits or altered serialization behavior.

Could you confirm:

Approx. size of the base64 payloads that fail

Whether small payloads also fail or only larger ones

Request format (JSON with embedded base64, etc.)

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MV-01071313-0 2 on at

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Payload size: the failure happens regardless of size. We tested both small files and larger ones (e.g. a PDF 64KB before base64 encoding, about 90KB once encoded in the request body), same 500 error in both cases.

Small vs large: small payloads fail too, not just larger ones, regardless of file weight.

Request format: JSON body, with the file content included as a base64 string in one of the request fields (per the Anthropic Messages API schema via Azure AI Foundry). The request structure hasn't changed compared to the working tests from June 26-29.

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