Thank you for your reply.
Sorry to have written in French, it didn't translate.
I activated the payment plugin, and configure (Paypal, Stripe and Mollie) but nothing is displayed. I do not understand, however I have already changed browser, computer and even try via a mobile phone. I also changed PHP version several times, but nothing changes.
Concerning the live, I have my site which is in HTTPS, and I tried with Google Chrome, Mozilla, Internet Explorer and Opera, but it still does not work. I am a little lost.
Thank you