Knowing when a message was successfully sent from the device is important because it provides opportunity for you to inform your user that his/her message was transmitted with success.

When you need to know if a message was delivered successfully to the PubNub Cloud via Socket.IO, you will use the acknowledgement callback argument. This function must be placed in the correct place in order to work properly. The video demonstrates the correct usage.

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Socket.IO on PubNub - github.com/pubnub/pubnub-api/tree/master/socket.io

PubNub Website - pubnub.com/

GitHub Repository - github.com/pubnub/pubnub-api/