webhook sending empty object

I’ve written a simple script to receive data from a webhook and write it to a google sheet as a new row. However, the google sheet is only receiving an empty object (i.e. “{}”). Every form submit results in a new row containing “{}”.

I’m following this tutorial.

I’ve deactivated all non-essential plugins. I’ve deleted and re-installed the plugin.

The page I need help with: [log in to see the link]