Hello Nathalie,
Probably that’s not the reason.
Now the PHP file seems to be with the correct code. Maybe you defined wrong $apiKey or $listId. Can you please re-check ? We did a test now with the code we distribute for the newsletter form and it’s working.
Case still no success, please give to us temporary FTP access to your server files (host, username and password). Also share with us the API KEY and LIST ID from your Mailchimp account. This way we can debug the code in your server to discover where’s the issue.
You can send these credentials as private message here, so it will not be public.
Kind Regards,
Rodrigo.
If you are satisfied with Porto HTML and our support, please leave your comment and rating on ThemeForest downloads page. That helps us a lot: https://themeforest.net/downloads