8.5 years later...
The "company account" value is the subdomain that you access the Method web ui through for your company (or the one you are setting up the api implementation for). If you can access the ui, you have this "keyword".
When you login to your account in a browser, you have to go to <something custom>.method.me. That first custom part of the url is the "Company Account".
For whatever reason, the documentation (and other info on this) is extremely nebulous.