1. When I try to add an account or when I switch to the staging server I see the "Error in cURL request: SSL certificate problem: unable to get local issuer certificate" error message

This problem is not specific for this package, but usually means that your PHP installation is not configured correctly.

A little digression is needed here: if not otherwise specified, when PHP (via a component called cURL) connects to HTTPS websites, it verifies that the SSL certificate of the website has been issued by a reliable certification authority.

The above error message means that PHP could not verify the reliability of a certification authority.

In order to fix this you have two options.

The first solution is to disable the certification authority reliability verification. This is hightly discouraged for security reasons, and can be achieved bu running the "c5:config set app.curl.verifyPeer false" console command (see this documentation page to know how to use concrete5 console commands).

The second solution (highly recommended) is to fix the reliability verification and is very easy:
- download the list of reliable certification authorities (it's the cacert.pem file available here) and save in a directory of your web server (let's assume you saved it as /var/www/ssl/cacert.pem)
- add to your php.ini file this configuration line: curl.cainfo=/var/www/ssl/cacert.pem
- reload the webserver (Apache/nginx) configuration (for instance with Ubuntu: "service apache2 reload")