If your email service provider is not configured to use a secure connection, you will see an error like this:
If you ignore this warning, your visitors will likely get an error message on Facebook, and after they opt-in if they are using the Firefox or Safari browsers (based on their security settings).
Leadpages are served from a secure platform (SSL):
This includes all images, scripts and our HTML code. We never redirect or send information via unencrypted HTTP protocol. The only situation in which we send people from the HTTPS to HTTP is when the email marketing service uses HTTP (i.e., sends data without encrypting it) in its forms.
Based on this, you will need to contact the support team for your email service provider to resolve this issue.
(Updated March 21, 2017)
Please let us know if you have additional questions.
You can always file a support ticket if you have additional questions by clicking the Support button in your dashboard shown here or clicking here to file a support ticket.