My clients are not redirected properly... they get a 404 "page not found" error
1. You should Update your Permalinks.
Please check your Permalinks settings if it is changed to "Post Name". Even if they are already set to "Post Name", go ahead and re-save it to reset.
2. Check your Theme Link Pages
Additionally, you need to verify that all of the WP-Client Theme Link Pages are correctly installed and linked in WP-Client → Settings → General → Theme Link Pages (you should see green checkmarks next to all of the boxes).