MyTime Import says the file is not a database. What should I use?

MyTime Import needs an original .mytimedb backup created by MyTime. A PDF, text export, WitnessWork JSON backup, or a file renamed to .mytimedb will not work. To get one, go to More → Settings → Backup in MyTime and email yourself a backup, then save the attached file on your device and select it through Settings → Import Data → From MyTime. Keep the original file unchanged. If a valid backup still fails, email support privately with the error and app version; do not post the backup in a public issue.