Viber on iPad mini won’t sync to iPhone

I realized Viber on my iPad was missing messages that were on my iPhone. Also for some reason Viber, which is set to back up daily, hadn’t backed up for 3 months. So I updated the app on iPhone, backed it up to iCloud, and went to re-install on the iPad mini and there’s nothing there. No old messages no contacts nothing. But it’s fine on the iPhone. How do I get viber on iPad to sync with my iPhone?