"There was an error loading the file" error when uploading file with "http"

Hi,

I’m receiving this error when I attemp to upload an audio file to a PHP server.
I don’t know is this is a response from the server or a plugin error.

My code:

this.http.uploadFile(this.serverurl + "upload.php",  {}, {}, this.file_path, "file")
        .then((response) => {
          this.successCallback(response);
        })
        .catch(error => {
          console.log("status: " + error.status);
          console.log("error: " + error.error); // error message as string
          console.log("headers: " + error.headers);
          console.log("body: " + error.body);
          console.log("type: " + error.type);
        });

“serverurl is defined
"file_path” is like “file:///storage/emulated/0/Android/data/com.xxxx.xxxx/audio.m4a”

This is what I get in the console:

status: -1
error: There was an error loading the file
headers: undefined
body: undefined
type: undefined

The webservice is OK because I tested it with Postman.

Maybe I’m doing something wrong in the code. Please help!
I can’t find any documentation about the “-1” status code, neither in the plugin docs or php docs.