Looks like you struck the same issue with Mint that I did, where 'libssl1.0.2' isn't installed.
Assuming you are on an Intel/AMD 64-bit platform then you can download its Debian package from the command line using:
wget http://ftp.us.debian.org/debian/pool/main/o/openssl1.0/libssl1.0.2_1.0.2u-1~deb9u1_amd64.deb
then run:
sudo apt-get install ./libssl1.0.2_1.0.2u-1~deb9u1_amd64.deb
sudo apt-get install netxms-agent
That should get the agent installed.
				
			Assuming you are on an Intel/AMD 64-bit platform then you can download its Debian package from the command line using:
wget http://ftp.us.debian.org/debian/pool/main/o/openssl1.0/libssl1.0.2_1.0.2u-1~deb9u1_amd64.deb
then run:
sudo apt-get install ./libssl1.0.2_1.0.2u-1~deb9u1_amd64.deb
sudo apt-get install netxms-agent
That should get the agent installed.