I cannot send and receive messages from another user of Zoiper 5.
Make sure that the contact to whom you want to send a message is added properly into Zoiper. His phone number/ extension should be added in the "ipPhone" field.
I suggest that you take a look at our guide for messaging here: https://www.zoiper.com/en/support/home/article/209/How_to_use_IM_%28chat%29_and_Presence_with_Zoiper_5#windows
Also make sure that your VoIP service provider support SIP "MESSAGE" messages.