No webhook response from Acumbamail

I'm trying to create my first automation in Pabbly. The trigger is adding a new subscriber in Acumbamail (I have a paid account there).

I set up the webhook in the Acumbamail list settings, tried adding a new subscriber several times, but nothing happens – I'm stuck at "Waiting for webhook response".

Any ideas how to fix this?

Never mind. It turns out that when I was adding a new subscriber manually in Acumbamail, the webhook didn't detect them. However, when an actual subscriber joined, it worked.