SSO Isssues – Login Not Passed to FD Site

Hello. I have tried uninstalling, reinstalling, and re-configuring the FD plugin for our WP site, but nothing has caused SSO to work correctly.
I have triple checked all shared secret, portal URL, etc., and they are all correct per the documentation.

Example:
After entering credentials on WP site, the user is not redirected to the FD site. Also, upon manually revisiting the FD site, the login link is still displayed because the successful login is never passed back to the FD Portal. Effectively this is a loop, where our customers try to login, complete the login successfully and get redirected to the WP site/homepage, visit the FD site manually, and are then sent to log in again on the WP site. No matter how many times a user successfully authenticates to our WP site, the login is never passed back to the FD site.

Please let us know what to do to move forward in troubleshooting this issue.