How to fix "invalid return_url" error when creating oauth token for Trello with httr?

I want to manage my Trello cards and boards using the trelloR package but when I try to create a token with the get_token function, I get an error message on my browser : "Invalid return_url".

my_token <- get_token(key = my_key, secret = my_secret)

my_key is my personal Trello API key and my_secret is my OAuth secret. I got them on the Trello page that gives you your authentication codes, after login : https://trello.com/app-key

To use the Trello API and to access to boards, I need a token. This token is generated with OAuth1.0 by the httr package. Indeed, the function get_token do something like this, according to Jakub Chromec, author and maintainer of trelloR here :

trello.app = httr::oauth_app(
  appname = "trello-app",
  key = my_key,
  secret = my_secret)

trello.urls = httr::oauth_endpoint(
  request = "OAuthGetRequestToken",
  authorize ="OAuthAuthorizeToken?scope=read&expiration=30days&name=trello-app",
  access = "OAuthGetAccessToken",
  base_url = "https://trello.com/1")

httr::oauth1.0_token(
  endpoint = trello.urls,
  app = trello.app)

When I execute this code or the function get_token with my personal key and secret, I am redirected to my browser, which is normal. As described on this page, a screen should appear asking me to allow authentication. But instead I just have an error message in the browser : "Invalid return_url".

In the RStudio console, this remains displayed :

> my_token <- get_token(my_key, my_secret)
Waiting for authentication in browser...
Press Esc/Ctrl + C to abort

I'm using httr 1.4.1, curl 4.2 and trelloR 0.6.0 with R 3.6.1 under macOS 10.15.