Handle multipart/form-data in logic app standard Http action

Question

In logic app standard, I'm following this MS learn page to call an api with multipart/form-data body from the previous "Create_CSV_table" action:

https://learn.microsoft.com/en-us/azure/connectors/connectors-native-http?tabs=standard#content-with-multipartform-data-type

On the right side is the sample config while on the left is mine:

This returns a httpStatusCode 500: Outgoing HTTP request ends with server failure.

From raw input I can see all variables are parsed correctly (the body is simply the header row of the CSV):

    "method": "POST",
    "headers": {
        "Api-Key": "xxxxxxxxxxxxxxxxxxxxxxxx",
        "Authorization": "*sanitized*"
    },
    "body": {
        "$content-type": "multipart/form-data",
        "$multipart": [
            {
                "body": "Employee ID,Time Off,Date,Hours,Timestamp,IsDeleted\r\n",
                "headers": {
                    "Content-Disposition": "form-data; name=file; filename=LeaveDataTest.csv"
                }
            }
        ]
    }

After reading William's post here, I also tried replacing the body inside the $multipart with

"body": {
	"$content": "Employee ID,Time Off,Date,Hours,Timestamp,IsDeleted",
	"$content-type": "text/csv"
}

But this returned BadRequest - The provided workflow action input is not valid.

I tested the endpoint with Postman which supports attaching a physical file and that's the only thing worked. From the working call's snippet, there's a boundary added and encoding used, but I assume the Http action in logic app would do the same under the hood?

boundary = 'wL36Yn8afVp8Ag7AmP8qZ0SA4n1v9T'

dataList.append(encode('--' + boundary))

dataList.append(encode('Content-Disposition: form-data; name=file;')) Please explain a bit more as the original MS documentation is too brief.