"This site can't be reached" when I try to go to simplebooking.it

Thanks again. It appears that your computer is relying on your local router to get its DNS information. DNS can be described as the Internet's phone book. It takes those URLs and converts them to the remote site's actual IP addresses.

Please give the following a try. You will be entering a command into the Terminal app. That command is called "ping." It is used to verify connectivity over a network.

To do so, you will find the Terminal app in the /Applications/Utilities folder on your Mac. Go there, and then, run that app. It should open up in a window that has a command prompt waiting for you to enter commands.

At that prompt, enter: ping -c3 192.168.1.1, and then, press the return key. The results should looks something like the following:

There should be a total of 3 pings going to your router's IP address. A successful ping would result in all 3 ping packets being transmitted & received back, with 0.0% packet loss.

With the Terminal window still open, enter the following command, followed by the return key: ping -c3 simplebooking.it

Here are the results I get when doing so:

Again, notice that the simplebooking.it URL is transformed to the site's IP address: 62.48.39.93. It is pinged 3x with 0.0% packet loss. That, again, would be a successful result.

You don't have to post any screenshots of your results, just let us know if the pings were successful, or not.

To exit the Terminal app, enter: exit, and then, press the return key. You can then just close the Terminal window.