I accidentally closed the browser during formatting.

Nothing was lost to us, because formatting happens entirely in your browser — there was no upload in progress to corrupt. Just reopen the tool:

1. Go back to My Books (same browser) and open your book.
2. If your manuscript isn't still loaded, load the DOCX again.
3. Re-run the format and export.

Formatting is quick to redo. If your book itself is missing after the browser closed, that's a storage issue, not the interruption — see My project disappeared. And keep a project-file backup so a stray close is never a worry.