Why can I not get the iCloud automatic backup switch to turn on in settings?

[iMore Question]

On my New iPhone 7Plus running ios 10.0.3. I've tried in setting up iCloud backup , Settings / iCloud I can not get the Backup to turn on. I have plenty of storage space in iCloud. I believe all other backups have been completed from other iphone 6plus. I can't figure it out.