tmeessen on "[Plugin: Participants Database] Using variables subscription confirmation email"

Hello,
I have been using the Participants Database plugin for 2-3 years. I made a recent version update of the plugin and since then, I am encountering one regression problem.
Previously, I add to configure the [pdb_signup_thanks] to use variables referring to fields, with a text such as: "Thank you [first_name] for your subscription in the category [category]...."
Since the last update, the variable don't seem to work anymore.
Did I miss something in the new version documentation?
Cheers,
Thierry

https://wordpress.org/plugins/participants-database/