To find a database ID, open the database in your Notion workspace and look at the URL. The ID is the string of characters between the slash after the workspace name (if there is one) and the question mark, a 32-character alphanumeric string.

Databases with more than one data source

A Notion database can hold several data sources, which are the separate tables that live inside one database. Most databases have exactly one, and for those nothing changes.

If yours has more, the plugin writes to the first one and the Notion tab of your form shows a notice listing every data source it found, each with its own ID. To write to a different table, copy the ID from that notice and paste it into the Database ID field instead of the database ID. Both kinds of ID are accepted.