title: Subscription Frequency and Price Change hook in Woocommerce Subscriptions
body: <p>Maybe I overlooked it, but as much as I searched, I could not find which <code>action</code> to hook when a subscription changes price or frequency in Woocommerce Subscriptions.</p>
  <p>The <a href="https://docs.woothemes.com/document/subscriptions/develop/payment-gateway-integration/" rel="nofollow noreferrer">documentation</a> says that to support price changes in your payment gateway you have to list <code>subscription_amount_changes</code>, but nowhere it says which function will be called when the amount actually changes..</p>
  <p>Also in the <a href="https://docs.woothemes.com/document/subscriptions/develop/action-reference/" rel="nofollow noreferrer">Action reference</a> I was unable to find an action hook which is called when the subscription amount or frequency changes. If anyone has a clue which hook to use or how to implement this particular feature, please tell me.</p>
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  <h2>Edit</h2>
  <p>Ok thanks for the comments and answer by @Reigel, so if I understand correctly the change of a subscription in the admin menu (which I indeed refer to), has to be handled by the <code>save_post</code> action. Could you provide a small example how to hook this action and check if it is a subscription and get the <code>$order_id</code> (I guess this is the same as <code>post_id</code>?) to use in the subscription management calls?</p>
  <p>Thank you very much already!</p>