Impossible to send email

Dear,

I’m using Contact Form 7 version 5.5.6 with WordPress 5.9.3 and since a few time, I can’t send emails and have the following message “Une erreur s’est produite lors de l’envoi de votre message. Veuillez essayer à nouveau plus tard.” ?

What could be the problem and how to fix it please ?

Thank you in advance for your answer.

The page I need help with: [log in to see the link]