'Send_an_HTTP_request' failed (possibly) because of "attachments" property

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Posted on by tolga-balci

Hi Everyone,

I created a flow to get an XLSX file from a OneDrive folder, and use it as an attachment.

I save the attachment details in a JSON variable named fileAttachment (as follows) to use in my HTTP call:

{
"name": "Monthly Report-Windows.xlsx",
"contentBytes": "<base64(content Bytes)>",
"contentType": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
}

I'm then using the following HTTP call - the Content-Type is set to application/json:

{
"subject": "Here is your monthly report",
"body": {
"content": "Here is your monthly Windows report as requested."
},
"toRecipients": [
{
"emailAddress": {
"address": "customer_to@customer.com"
}
}
],
"ccRecipients": [
{
"emailAddress": {
"address": "customer_cc@customer.com"
}
}
],
"attachments": [
{
"@odata.type": "#microsoft.graph.fileAttachment",
"name": "variables('fileAttachment')?['name']",
"contentType": "variables('fileAttachment')?['contentType']",
"contentBytes": "variables('fileAttachment')?['contentBytes']"
}
]
}

This HTTP call returns the following error:

{
"error": {
"code": "BadRequest",
"message": "Unable to read JSON request payload. Please ensure Content-Type header is set and payload is of valid JSON format.",
"innerError": {
"date": "2025-01-23T13:26:54",
"request-id": "",
"client-request-id": ""
}
}
}

However, if I take out the "attachments" property from the call, the HTTP call works perfectly. Following is the JSON that works without any issues:

{
"subject": "Here is your monthly report",
"body": {
"content": "Here is your monthly Windows report as requested."
},
"toRecipients": [
{
"emailAddress": {
"address": "customer_to@customer.com"
}
}
],
"ccRecipients": [
{
"emailAddress": {
"address": "customer_cc@customer.com"
}
}
]
}

That means, the code that is causing the error is with the "attachments" property. I've run the JSON call through various linters, and there is no issue with the JSON structure.

I'm trying to understand what causes the error, but unfortunately no luck so far.

Any ideas?

Thanks!

Tolga

Edit: Formatted code.

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Suggested answer

Ellis Karim 11,990 Super User 2026 Season 1 on at

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Hi @tolga-balci

Try the following for the attachment array:

{ "name": "Monthly Report-Windows.xlsx", "contentBytes": { "$content-type": "<contentType>", "$content": "<content>" } }

📝Best Practices for Formatting File Attachment Arrays in Power Automate: Approvals, Outlook, OneDrive & SharePoint – Ellis Karim's Blog

Ellis Karim
Blog | LinkedIn

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tolga-balci 72 on at

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Hi @Ellis Karim,

Thanks very much for your reply, but unfortunately I could not get your solution to work.

However, I found out the time (after a week) to create a solution.

In my initial post:

I converted the attachment contentBytes to <base64>. It was wrong. I converted it to @body('<name>')['$content'].

"contentType" property under "body" was missing. I added it.

"importance" property was missing, I added this one as well.

I did not check if any of those are required attributes for a successful HTML call, causing an error.

For anyone who needs a tl;dr answer, below is a template that you can use:

{ "subject":"", "importance":"", "body":{ "contentType":"HTML", "content":"" }, "toRecipients":[ { "emailAddress":{ "address":"" } } ], "ccRecipients":[ { "emailAddress":{ "address":"" } } ], "attachments":[{ "@odata.type": "#microsoft.graph.fileAttachment", "name": "", "contentBytes": "" }] }

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