Jess Documentation
Squarespace Form SetupInstalling Form Conversion Tracking Code on Squarespace Websites
From the Squarespace Dashboard:
Settings, click Advanced, and then click Code Injection.
Paste the Jess code into the footer section.
Click Save
If you are using a custom configured form, you can add code to the form by clicking Pages, navigating to the page, clicking Settings (the gear icon) and then Advanced.
Pages, choose the page, click Settings (the gear), Advanced. Paste the code into the box and click Save.