An online communication session invitation request message for an online communication session is received from an initiating client computing device. The invitation request message includes connection data of the initiating client computing device and an online communication session endpoint identifier of an intended participant of the online communication session. The session endpoint identifier is associated with a plurality of push tokens that correspond to a plurality of recipient client computing devices respectively. An invitation request message is sent in the form of a push notification message to each of the plurality of recipient client computing devices using the corresponding push tokens. Each invitation request message includes the connection data of the initiating client computing device.