What are they ?
In order to take action on your behalf, Phantombuster needs to authenticate as yourself. For that purpose, it needs (some of) your session cookie(s).
These are one strings of text generated by the websites you connect to when you login and are stored on your computer.
Phantombuster doesn't know your password, nor your email address and those cookies resets when you manually log-out of a website.
How to get your cookies manually
Open a new tab and go to the website whose cookies you're after.
Right-click anywhere on the page and open the inspector:
Locate the “Application” tab
Then select "Cookies" > http://www.websiteyourafter.com
Locate the cookie you're looking for.
So for example, for LinkedIn, you'll be looking for the li_at cookie's value...
...and paste it back in your Phantombuster's API configuration.
You're all set!