You will initially receive your customer number by e-mail as soon as your user account has been activated.
If you no longer know your customer number, you can log into the customer portal at https://appload.scopevisio.com/apps/public/login.html.
There you will find the customer number of your Scopevisio instance.
As a rule, your customer number is also the same as your instance number, which you can find via
F12 (Windows systems)
System menu > Info > About Scopevisio
System menu > Settings > General > Info