Connecting to a MSSQL Server 2016

My situation in the local network:

• I’m working on a iMac
• the Testserver is a Windows Webserver 2016 (192.168.16.6)
• the SQL Server is MS SQL Server 2016 (192.16.16.5 on Port 1433)

I have a local directory for my site on my Mac

I am connected to a MS Windows Webserver via FTP.

The connection and uploading works fine.

Now my problem:
I can not figure out how to make a connection to MS SQL Server with Server Connect. I always get an error:

“Error using Database Connection! Can not connect to database! Check your network or server address”

The connection with SQLPro Studio does work without problems.

I’m using asp.net, any idea what could be the problem?

Thanks for your help in advance.