The user is forced to return to their home that does not have a valid ssl certificate.

Hello,

After I tick Enable PayPal Pro and save the settings, users who log in to upgrade their website, will see the status bar and crossed the red SSL. This shows that my website is not secure, even though I already install an SSL certificate. SSL certificate is required to enable the function Paypal Pro. The problem users began to doubt my website. How I can set the page is secure? Users also have difficulty returning to their home, because there is no click buttons that allows them to return to their home. When they click on their profile, they are forced to return to their profile pages with warning signs that their site is not secure. Can anyone help?