I want to apply my skin from a png file with the mojang/minecraft java api

I’m trying to apply a skin with a file, and I did everything according to the mojang api docs (https://mojang-api-docs.gapple.pw/needs-auth/change-skin) but it keeps throwing a 500 Internal Server Error. Does anyone know why? It works when applying from a url but not from a file

import requests
import base64

file_path = 'F:\!! Chrome Downloads\'
skin_file = 'ec588a08f5eb3c6d.png'

full_path = file_path+skin_file

url = 'https://api.minecraftservices.com/minecraft/profile/skins'
auth_token = <authorization>

def png_file_to_binary_file(file):
     with open(file, "rb") as f:
        png_encoded = base64.b64encode(f.read())
        encoded_b2 = "".join([format(n, '08b') for n in png_encoded])

        return encoded_b2

binary_png = png_file_to_binary_file(full_path)

headers = {
    'Authorization':auth_token,

}
payload = {
    "variant": "slim",
    "file": binary_png
}


req = requests.post(url=url,headers=headers,data=payload)

print(req.status_code)
print(req.reason)
print(req.text)