The text refers to the two exchanges being Subscription request  Subscription confirmation For the subscription confirmation there are indeed two channels, but that is not what the text refers to.  Suggestion is to reword the phrase to make this more clear:   Existing wording:    Subscribing consists of two exchanges: Subscriber requests a subscription at the hub.url url. For hub.channel.type = webhook , Hub confirms the subscription was actually requested by the subscriber by contacting the hub.callback url. For hub.channel.type = websocket , Hub returns a wss url and subscriber establishes websocket connection. Unsubscribing works in the same way, except with a single parameter changed to indicate the desire to unsubscribe. Proposed wording: Subscribing consists of two exchanges: Subscriber requests a subscription at the hub.url url. The hub confirms the subscription was actually requested by the subscriber. This exchange can be implemented in two ways depending on the channel type. For hub.channel.type = webhook , Hub confirms the subscription was actually requested by the subscriber by contacting the hub.callback url. For hub.channel.type = websocket , Hub returns a wss url and subscriber establishes websocket connection. Unsubscribing works in the same way, except with a single parameter changed to indicate the desire to unsubscribe.