Autoresponder doesn't exist error when signing up from Facebook

I just realised recently that the sign up form on my website is throwing an error when people are opening my website and signing up from their iPhone Facebook mobile app (not sure about Android). And this is the message:

Oops!
We’ve run into a problem — please see if you can fix it!
Autoresponder doesn’t exist or has been deactivated. This is a permanent error. Cannot continue.

My sign up form works fine when signing up from a web browser on a computer or on a mobile device.

Form action: https://app.getresponse.com/add_subscriber.html
E-Mail field: email
First Name Field: first_name
Hidden Fields:

<input type="hidden" name="campaign_token" value="nnZP3" />
<input type="hidden" name="start_day" value="0" />
<input type="hidden" name="thankyou_url" value="http://chinesetalkeze.com/signup-thank-you"/>

Here’s the page to my sign up page:
http://www.chinesetalkeze.com

To test from Facebook app:
1. search for Chinese Talkeze in facebook and go to my facebook page.
2. click on my website link to go to my website from facebook app
3. sign up using the red sign up box (enews extended)
This will give you the error mentioned above.

How do I fix this?

https://wordpress.org/plugins/genesis-enews-extended/