Problem with authentication

[NikKOo31]

Hello! I'm having problems with the authentication of the client (I think).
So far I've tried the methods from the examples:

const client = new ImgurClient({ clientId: MY_CLIENT_ID });

const client = new ImgurClient({ accessToken: MY_ACCESS_TOKEN });

const client = new ImgurClient({
  clientId: MY_CLIENT_ID,
  clientSecret: MY_CLIENT_SECRET,
  refreshToken: MY_REFRESH_TOKEN
});

I'm able to upload a few images, but then I start getting error messages in the response:

{"data":"Invalid client_id","status":403,"success":false}

{"data":"The access token provided is invalid.","status":403,"success":false}

And after a few retries I get this one:

{"data":"","status":504,"success":false}

Which would be the best method to authenticate? I'm using Node JS btw
Thanks!