Mixed content errors occur when your HTTPS site loads resources over HTTP.
For example: https://example.com loads http://example.com/style.css
Common Cause
Your WordPress database may still contain HTTP URLs instead of HTTPS.
How to Fix It
Install the Better Search Replace plugin.
Search for:
http://your-site.comReplace with:
https://your-site.comSelect all tables.
Uncheck Run as dry run.
Click Run Search/Replace.
This will update all HTTP URLs in your database to HTTPS.
Final Step
After the replacement, go to FlyingPress and click “Purge & Preload Cache” to clear old cache and ensure the new HTTPS URLs are used.
You can safely uninstall the plugin once done.