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I have created a 'Subscribe' page using the provided code within my Sendy installation. However, I am unclear on how I can add additional fields (i.e. 'What List Do You Want To Subscribe To?', An Active Subscriber Count and 'I Am At Least Thirteen Years Of Age'). How would this look within my code?
I can see you're not technical judging from your last question and this, but that's fine. For custom requirements like this, you need to hire a developer to program this for you using Sendy's API.
Sendy's support does not cover custom programming. You can PM @vincentpolisi to get a quote or find help at http://www.odesk.com.