No need to use a third tier app on mac. I’m still running under mavericks (10.9) and it works perfectly well with Screen Sharing app which come bundles with OS X.
Are you trying to remote control the pi from outside your network or from inside ?
If it’s from inside your network, the ip address you typed seems not good (class A IP address), in most cases it will be something like 192.168…
By the way, why not setting a static internal ip for your pi and configuring the DNS so the static ip always point to a hostname, something like osmc, so when you try to connect from inside your network, you only have to type
If you are trying to control it from the outside, you’ll need to configure port forwarding on your router and you’ll need anyway to set a internal static IP for the Pi, it is mandatory.
Further more If your ISP use Dynamic IP addressing (meaning your external IP change everytime the router restart) you will need to configure Dynamic DNS on your router, and configure a client on your router or pi to update the IP address with the DynDNS service.