How to insert uploadUrl to this FFUploadedFile costum code?

I need to insert on my custom code of FFUploadedFile, the uploadUrl property that i read on:
https://community.flutterflow.io/discussions/post/docs-for-ffuploadedfile-SmomdvrPyNigeWG

Anyone knows how to do it properly? The code from my costum action is bellow.
I mus to do it, because my API from Whatsapp, only accept a file from frontend in this way, and it's error response is here:
{

"error": true,

"code": 500,

"message": "TypeError: Cannot read properties of undefined (reading 'mimetype')"

}

I don't have a clue how to insert mimetype properly on FFUploadedFile, my guess is thath if can insert the url, the API will get the mimetype from there.

import 'dart:convert'; Future<FFUploadedFile> base64ToFFUploadedFile(String base64String) async { // preciso de uma ação que transforme uma string de base64 em um FFuploaded File // Decodifica a string base64 final bytes = base64Decode(base64String); // Cria um ffuploadedFile com os bytes decodificados final ffuploadedFile = FFUploadedFile( bytes: bytes, name: "image.png", ); // Retorna o ffuploadedFile return ffuploadedFile; }