Use this API call to change the subscription plan of a subscriber. A subscription plan is specified; the most recent version of that plan is used.
This call does not do any prorating, it doesn't generate an invoice, it doesn't notify your customer, it doesn't affect your customer's active_until, and it doesn't charge them anything. Your customer's feature level is immediately changed to that of the new plan. The next time your customer is renewed, we'll use the details of the new plan to do it.
Do an HTTP PUT like so:
[ ~ ] $ curl -i -u 28068fe710ed67dd38de8bcd48b0544cbabcfb03:X \
-X PUT -H 'Content-Type: application/xml' \
-d '
<subscription_plan>
<id>13</id>
</subscription_plan>' \
https://spreedly.com/api/v4/meresheep/subscribers/44/change_subscription_plan.xml
If successful, a 200 (OK) status code is returned.
A 404 (Not Found) status code is returned if the subscriber is not found.