The HTC Backup service is no longer available in HTC phones that use Android 6 Marshmallow or higher.
HTC Backup has been renamed as HTC Restore. With this service, you still can restore previous backups saved by HTC Backup to your phone.
You need to download and use the HTC Restore app on your phone to access these backups.
Use your Google
Account to automatically back up your phone to Google Drive. You can also use your your Google
Account when restoring your backup from Google Drive to a new phone.
See the user guide or how-tos for details.