title: Changing the Amount of a PayPal Subscription
body: <p>We are using PayPal subscriptions to automatically make ongoing monthly donations.  The user initially creates a subscription with some pre-determined monthly donation amount (e.g., say $50/month).   This creates a recurring subscription which we process by way of IPN. All good there.  But, our interface allows the user to come in and change their monthly donation amount, say from $50/month to $100/month.   I am wondering how I can change the PayPal subscription to reflect this new amount?</p>
  
  <p>There is a method in PayPal's NVP API called "UpdateRecurringPaymentsProfile" which says I can update the subscription amount, but unfortunately it says:</p>
  
  <p><em>For recurring payments with Express Checkout, the payment amount can be increased by no more than 20% every 180 days (starting when the profile is created).</em></p>
  
  <p>(reference: <a href="https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&amp;content_ID=developer/e_howto_api_nvp_r_UpdateRecurringPaymentsProfile" rel="noreferrer">https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&amp;content_ID=developer/e_howto_api_nvp_r_UpdateRecurringPaymentsProfile</a>)</p>
  
  <p>To be honest, PayPal's API's are quite confusing so I'm not sure if I am using the Express Checkout or not.  (We are creating Subscription buttons using the simple Website Payment Standard API).</p>
  
  <p>Will this work? If not, is there an alternative to achieve what we need?</p>
  
  <p>Thanks!</p>