SSO integration issue

Hi,
im new in the OKTA. i need to create a app in OKTA with single sign-on for connecte my site.
I have installed the simplesamlphp in my server. we also changed the site as https.
when we click the app, my site will open using with OKTA credential. we are getting “Invalid Key”.
Anybody have proper sso integration,please share.

Thanks&Regards,
Durai