If you have created a popup and published it, but visiting its preview link or triggering it results in a "404 Page Not Found" error, it means WordPress rewrite rules need to be refreshed.
How to Fix 404 Errors:
- Log in to your WordPress Dashboard.
- Navigate to Settings > Permalinks in the left sidebar menu.
- Scroll to the bottom of the page and click the "Save Changes" button.
- You do not need to edit any settings; simply clicking save will refresh the WordPress URL rewrite database.
- Visit your popup preview again; the 404 error should now be resolved.