[Python] passing a csv through an API

I'm trying to pass a csv through an api like this:

The csv is as follow:

field_1, field_2, field_3
1, 3, 7


the push code is this:

with open("sample_csv.csv") as f:
data = {"file": f}
print(data)
headers = {
"Content-Type": "text/csv",
"File-Type": "POS",
"File-Key": "somekey",
}

r = requests.post(endpoint, data=data, headers=headers)


However when i read it from a Lambda on the other end i get this:

b'file=field_1%2C+field_2%2C+field_3%0A&file=1%2C+3%2C+7'


When i run the above string through chardet it tells me its ascii, but i dont know how to convert it


edit: lambda function code:

def main(event: dict, context) -> dict:
body = base64.b64decode(event["body"])
print(body)

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