Do I need an SSL/TLS certificate to use MemberPress?

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. 

While MemberPress doesn't require a security certificate for its basic use,
please note that some of our supported payment gateways, such as Stripe, Square and Authorize.net, do require one. 

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.