Online but can't receive viber messages

[WPCentral Question]

Hello. I am always online on viber (wifi in our house is always on) but for some reason, my friend cannot send messages to me. He told me that on his side, he can see "sent" instead of "delivered" on the message status which means that the receiver is offline, however, I am online. We were discussing about this but could not come up with a conclusion. Please help. Thanks.