When you encounter Error 400 (Bad Request) in the Jader.in app only when using WiFi but not mobile data, it typically points to an issue with your WiFi network or device configuration rather than the app or the website itself. This is supported by several common causes and solutions referenced in the search results:

- Network-Specific Issue: Since the error disappears when you switch to mobile data, your request is likely reaching the server correctly over mobile, but not over WiFi. This suggests a problem with your WiFi network setup or configuration rather than the app itself134.

- DNS Cache Problems: A corrupted or outdated DNS cache on your device or WiFi router can result in the server not understanding your request, which then triggers a 400 error. Try flushing the DNS cache on your device. On Windows, use ipconfig /flushdns; on macOS, use sudo killall -HUP mDNSResponder in Terminal246.

- Router or Device Issue: Temporary glitches with your router or device can interfere with network requests. Restart your WiFi router and your device to clear these issues14.

- Corrupt Cookies or Cache: Sometimes, the cached data or cookies stored in your device for that app or its web components could be corrupted, especially if you use the Jader.in app through a webview or browser. Clear the app cache and data, or clear your browser’s cache if you use a web interface34.

- Mismatch or Conflict in Network Settings: If your WiFi is using a VPN, proxy, or custom DNS that your mobile data doesn’t, this could be causing the issue. Disable VPNs or proxies to see if the error resolves1.

- Check for Browser/App Updates: Ensure your browser or the Jader.in app is updated, as outdated software can sometimes cause protocol mismatches resulting in 400 errors34.

Steps to fix:
- Restart your device and WiFi router.
- Flush your device’s DNS cache24.
- Clear app or browser cache and cookies34.
- Disable any VPNs or proxy servers on your WiFi network1.
- Try connecting to a different WiFi network to rule out an ISP-specific issue.
- If the issue is with all apps/websites on WiFi, contact your ISP or network administrator for help14.

If the error only happens with Jader.in on your WiFi and nowhere else, it’s possible your ISP or router firewall is blocking or corrupting requests to that specific server, which would require network-level troubleshooting.

In summary: The 400 error over WiFi is most often fixed by refreshing network settings, clearing DNS cache, restarting devices, and checking for network-specific blocks or misconfigurations124.