I am facing this error when connecting ngrok to Blackeye operation in Ubuntu 20.04. This is when I input authentication token in the format "./ngrok authtoken *******" as provided in the ngrok website. Please assist. Note that I am an amateur user of Ubuntu..
It looks like you downloaded the wrong ngrok TGZ file for your CPU architecture. ngrok supports x86, ARM, MIPS, and a few mainframe architectures. If you go to https://ngrok.com/download and select Linux you'll see a dropdown. Make sure you select the one that correlates to your computer's CPU. Alternatively, you can also install via Apt or Snap. The commands for both are on the download page linked above.