Planny uses a special iCloud sync to sync between Watch and Phone, not the standard bluetooth sync. This enables more bandwidth and the transfer of more data and also enables Planny without iPhone over LTE.
iCloud Sync requires Planny Pro, so to sync your data you need to purchase on iPhone, iPad or Mac.
Complications don't automatically update, because this isn't possible with current technology provided by Apple. There are some time intervals available, when Planny will update the complications if network is good and battery isn't too low.