Can't connect to MS SQL Server

I'm trying to set up Peer-to-Peer Transactional Replication and I'm stuck at "Add a New Peer Node" step - I can't connect to another server.

In server name field I specify serverIP\DBNODE2 and SQL Server credentials.

I'm 100% sure, that credentials are correct, but I'm not sure about Server name part.

When I try to connect I get the following error:

Any ideas what am I doing wrong?