Cause: Your autoresponder sequence may not be active, or the campaign is not configured for autoresponder mode.
Fix:
In GetResponse, go to your campaign and make sure Autoresponder is enabled.
Verify that you have at least one autoresponder message set to send on Day 0.
The plugin sends dayOfCycle=0 with every subscription, which starts the autoresponder sequence from the beginning. If your first message is set to Day 1 or later, there will be a delay before the subscriber receives anything.
Tip: Set your GetResponse welcome email to Day 0 so new subscribers receive it immediately after subscribing through your funnel.