After a subscriber has chosen a subscription plan that gives them a free trial, they're no longer eligible for another free trial. If you'd like to allow a particular subscriber to be eligible for another free trial, do an HTTP POST like so:
[ ~ ] $ curl -u 2dac9d3d93326f97da4845d407789da232514b48:X -X POST https://spreedly.com/api/v4/meresheep/subscribers/444/allow_free_trial.xml
A 200 (OK) status code is returned on success. The xml of the subscriber is returned in the response body. In addition, the Location header in the response will be set to the url of the subscriber.