We deployed functionality to our network that allows you to disable leave events so you are not billed for those transactions unless you are actually using the Presence add-on. If you do not have Presence enabled, and you want to prevent the 402 responses, you must suppress leave events when you init the PubNub instance.
JavaScript SDK v4
var pubnub = new PubNub({ subscribeKey: "mySubscribeKey", publishKey: "myPublishKey", ssl: true, suppressLeaveEvents: true // <--- add this })
JavaScript SDK v3
pubnub = PUBNUB({ publish_key : 'demo', subscribe_key : 'demo', ssl: true, NOLEAVE: true // <--- add this })
The 402s should not affect your app negatively but if they do please report your incident to PubNub Support with the details.