Starting from FlyingPress v5, your pages are fetched from our cloud servers and rendered in a real browser environment. This enables FlyingPress to perform advanced optimizations such as removing unused CSS, detecting above-the-fold images, identifying images and fonts to preload, finding background images, detecting third-party scripts, elements to lazy render, etc.
These browser-level analyses allow FlyingPress to deliver highly accurate and effective optimizations for the best possible loading performance.
If preloading in FlyingPress isn’t starting or gets stuck, it’s usually due to connectivity or server restrictions. Here are the most common causes and how to fix them:
1. Site Is Local or Not Publicly Accessible
FlyingPress performs preloading from our cloud servers, so your site must be accessible from the internet.
Common scenarios:
The site is hosted on localhost or a private/staging server.
The domain is behind a VPN, firewall, or private network.
Solution:
Make sure the site is publicly accessible from the internet.
Preloading will not work in local or restricted environments.
2. Site Blocks Requests from FlyingPress Servers
Our preload servers are located in the USA, Germany, and Singapore. If your site blocks requests from our optimizer, preloading may fail.
Solution:
Whitelist requests where the User-Agent contains the keyword “FlyingPress” to allow FlyingPress Cloud Optimizer to access your pages:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/141.0.7390.54 Safari/537.36 FlyingPress (+https://flyingpress.com)
Here is a sample security rule in Cloudflare:
We don’t provide a fixed list of IPs to whitelist, as our server IPs can change when we add or remove servers. Whitelisting by the User-Agent keyword is the most reliable and future-proof method to ensure uninterrupted optimization.
3. REST API Is Disabled or Blocked
FlyingPress uses the WordPress REST API to manage and process the preload queue.
Solution:
Make sure the WordPress REST API is enabled.
Some security plugins disable or restrict REST API access. Check your security plugin settings and ensure the REST API is allowed.
The REST API must be accessible to non-logged-in visitors, as FlyingPress relies on public REST API endpoints for queue processing.
If you use a firewall, WAF, or hosting-level security rules, ensure REST API requests are not blocked or rate-limited.
You can verify everything is working by going to Tools → FlyingPress Queue → Test REST API and running the test.
4. HTTP Authentication Is Enabled
If your site requires HTTP Basic Authentication, our servers won’t be able to access it.
Solution:
Disable HTTP authentication.
5. Server Does Not Meet System Requirements
FlyingPress needs a compatible environment to preload properly.
Requirements:
Latest stable versions of WordPress, PHP, and MySQL/MariaDB
Standard file permissions
Standard WordPress folder structure
Solution:
Check that your server meets all FlyingPress system requirements.