Adding custom parameter to PayPal's smart button

Question

I'm making a subscription with Paypal, however the custom value I'm trying to create just isn't being received from the IPN from PayPal.

Therefore, I must be doing something wrong. To my knowledge, I'm passing the value correctly though?

This is my code, I'm trying to pass custom with my own value.

  paypal.Buttons({
      style: {
          shape: 'rect',
          color: 'gold',
          layout: 'vertical',
          label: 'subscribe'
      },
      createSubscription: function(data, actions) {
        return actions.subscription.create({
            'plan_id': 'P-000',
            'custom': 'custom value'  // the custom parameter attempt
        });
      },
      onApprove: function(data, actions) {
        alert(data.subscriptionID);
      }
  }).render('#paypal-button-container');

Answer 1

The parameter is documented as custom_id here: https://developer.paypal.com/docs/api/subscriptions/v1/#subscriptions-create-request-body

Unknown parameter names like custom will be ignored