Large files not accepted in AWS Ubuntu instance

Question

I am working on a Flutter app trying to upload images and videos to an AWS Ubuntu instance.

This is the function to upload the file to the server:

void _upload(File file) {
    if (file == null) return;
    setState(() {
    

    });
    String base64Image = base64Encode(file.readAsBytesSync());
    String fileName = file.path.split("/").last;

    http.post(phpEndPoint, body: {
      "image": base64Image,
      "name": fileName,
    }).then((res) async {
      print(res.statusCode);
      setState(() {
        print("***********SOURCE subido:"+this.source.toString());
        if(this.source.toString() == "MediaSource.image"){
          Toast.show(
              "Imagen subida", context,
              duration: Toast.LENGTH_LONG,
              gravity: Toast.CENTER,
              backgroundColor: Color(0xff01A0C7),
              textColor: Colors.white);
          incrementNumFotos(context);
        }
        if(this.source.toString() == "MediaSource.video"){
          Toast.show(
              "Video subido", context,
              duration: Toast.LENGTH_LONG,
              gravity: Toast.CENTER,
              backgroundColor: Color(0xff01A0C7),
              textColor: Colors.white);
          incrementNumVideos(context);
        }
      });
    }).catchError((err) {
      print(err);
    });
  }

This is the PHP script that receives and stores the sended file:

<?php
  $image = $_POST['image'];
  $name = $_POST['name'];
  $realImage = base64_decode($image);
  
  file_put_contents($name,$realImage);
  echo "OK";
?>

The issue that I am having is that the large files are not stored.

I have updated the file php.ini at the server:

upload_max_filesize = 128M
post_max_size =64M
max_execution_time = 300
max_input_time = 300

I have tried to upload files with different filesize.

A file with size = 5313566 bytes is uploaded. A file with size = 8891426 bytes is not uploaded.