Hi Robert,
In the User interface the list ID is in the URL.
If I open a srtatic list in Marketo for example the url might be :
https://app-xyz.marketo.com/#ST7808A1
#ST7808A1
ST stands for static list
7802 is the list ID
A1 is the tab in the UI
So in your case for this example you would be using just 7802.
Hope that does the trick.