Error 9403 can appear in Sync for two different reasons:
Sync can’t preview a file in the web panel (preview-specific issue)
Your web panel session is invalid or has expired (authentication/session issue)
Note: If you see Error 9403 while previewing a file, you can still download the file using the Download button in the web panel.
If you see Error 9403 while previewing a file
Error 9403 appears when Sync is unable to preview a file in the web panel. This is typically caused by a browser-related issue or a temporary loading error.
Try the following steps to resolve the issue:
Open Sync in a private/incognito window
This disables browser extensions and clears cached data that may interfere with file previews.Sign out, then sign back in
A fresh session can resolve temporary session-related issues.Temporarily disable browser extensions or ad blockers
Some extensions (especially privacy or security plugins) may block file previews.Try a different browser
This helps determine if the issue is browser-specific.
If you see Error 9403 when signing in or using the web panel
In many cases, Error 9403 is related to an invalid session, session expiry, or invalid login credentials. One common scenario is leaving the web panel open for a while, then attempting an action after your session has expired.
Try the following steps:
Refresh the page and sign in again
If your session expired, re-authenticating often resolves the issue.Confirm you’re using the correct email address and password
If credentials are incorrect, the session may fail to validate.Ensure your browser is up to date
Some users resolve this after updating their browser.Make sure JavaScript is enabled
Sync relies on JavaScript, and sign-in/session validation may fail if it’s blocked.Disable browser extensions (especially ad blockers / privacy tools)
Some extensions can block required scripts or challenges used during sign-in.Try a private/incognito window
This helps rule out cached data or cookie/session issues.Try a different browser or device
This helps confirm whether the issue is isolated to a specific browser environment.
Still having trouble? Contact support.
If the error continues after you've completed the troubleshooting steps, contact our support team with details about what took place when the error occurred so this can be investigated further.