Add SQL Target: unable do resolve network location

Hi guys, 

First time using SQL SENTRY.

I'm having this error message when I try to add my first target to monitor: "unable do resolve network location"

Network is working fine, from the server where Sentry is installed I can connect on the target host with Management Studio. 

Looks like something simple that I'm missing.

Here is printscreen: https://prnt.sc/UVOp3DgW-RZS

Thanks a lot.

Rafael