Update Contact field when Target Opens Email

 Hello everyone,  

I would like to trigger an autolaunched cadence flow to update a contact field , when the rule is " Email Open " in the positive track of the cadence.

When the flow is placed in the main track , we see the update on the contact field but the flow does not get triggered when placed in the positive track. (We added some wait time too so that contact gets enough time to open the email ). 

Is the "Email Open" cadence event tracked ??  

But when we check the Activity tab ,the Engagement tab

on the contact record we can see the contact opened the mail . 

So how does this "Email Open" rule in a cadence work ?  Will the cadence flow work alone or it requires coding to listen to this step happening . 

Any suggestions or guidance in the right direction will be greatly appreciated. 

Thanks