The Flipcause payment pages are all encrypted with bank-level security. They have a green lock icon on each of them that, when clicked, displays this certificate (this is standard on all payment processing pages across the web).
You'll also notice that all Flipcause tool URLs begin with "https," also indicating the SSL Certificate. Since all of your transactions will occur through Flipcause, your organization's website is not required to have the SSL. However, since 2017, Google and other search engines have started demoting websites that do not have SSL in their rankings and search results, so it is recommended for both the peace of mind of your supporters, as well as internet reputation, that you get SSL even though you are not technically required to have this additional certificate.
For more information about security, see here: https://www.flipcause.com/index.php/static_pages/security.