While a security certificate is
not required, it's definitely recommended.
Security certificates are what web browsers look for to place the green lock icon on the left of a site URL.
Seeing that may help your customers feel more confident about entering their personal data into your site.
For the exact SSL/TLS security requirements of those gateways, please contact their support directly.
Note: It's best to avoid security systems that allow you to selectively add SSL/TLS to your site. This can cause issues with the WordPress Login cookie discussed in greater detail here.