Hi there! I see you're trying to sign in using your driving licence and booking reference but keep hitting that error 15. Let's get to the bottom of this together.

Error 15 typically means that the system is blocking your request for some security reason—often related to firewall rules, network restrictions, or the system thinking the request might be automated (like a bot). This can happen due to certain network settings or browser issues.

Since you're using a WebKit browser on Android 10, let's try a few steps to resolve this:

1. Clear Browser Cache and Cookies:
- Go to your browser's settings.
- Find "Privacy" or "Storage" settings.
- Clear cache and cookies.
- Restart the browser and try signing in again.

2. Disable VPN or Proxy (if applicable):
- Sometimes, VPNs or proxies can trigger this error because they mask your real IP address.
- If you're using any VPN or proxy service, try disabling it temporarily.

3. Check Your Network:
- Switch from mobile data to Wi-Fi or vice versa.
- If you're on a corporate or school network, there might be firewall rules blocking access. Try a different network if you can.

4. Avoid Using Ad-blockers or Security Apps in Background:
- Security apps or ad blockers may sometimes interfere with communication between your device and our servers.
- Temporarily disable any such apps and try again.

5. Use the Official App if Possible:
- The Testi app is optimized for booking and managing driving tests without issues that browsers can sometimes encounter.
- Since you mentioned the error occurs during sign-in, if you aren't already, try signing in via the official Testi Driving Cancellations UK app.

If after these steps you still receive error 15, the issue may be related to DVSA’s security system suspecting unusual activity from your IP address. This sometimes happens if multiple attempts to book or manage tests come from the same IP within a short period.

In that case, wait for an hour or so before trying again, or try connecting through a different internet connection.

If none of these help, please feel free to share any other details about your situation, like which method (app or browser) you’re using or if you’ve tried these steps already, and I’ll assist further.

Are you satisfied with these suggestions so far?