Your Fullstory Org Id needs to be provided when configuring Fullstory using the Browser SDK NPM package and other client-side integrations.
Navigate to Settings > Data Capture and Privacy > Fullstory Setup and click Install your Fullstory snippet. You can find your Org Id embedded in the Fullstory snippet.
18PNWR.More information about installation and the data capture snippet can be found here.
Additionally, when you login to your Fullstory account, your Org ID can be found in the URL of your browser.
https://app.fullstory.com/ui/<ORG_ID>/home