How to view trial subscriptions that converted to paid subscriptions?

To view your subscribers who did not cancel before their free trial ended and subscribed - you'd want to use the Subscriptions export. You would download this export with a time range for when the subscription was created and a Subscription Status filter of "All." Once downloaded, you would compare the trial_ended_at date with the expires_at date. 

If the trial_ended_at date is earlier than the latter, this means the subscription converted from free trial to paid. If the trial_ended_at date is later or on the same date as the expired_at date, this means that the free trial never converted to a paid subscription.

If the trial_ended_at date field is populated and the expired_at date isn't, this means that either

1. The free trial converted to paid and is still active, or
2. The subscription is still in free trial and has not yet been canceled.

^ The scenario that applies depends on the date that the trial started. If you are looking at a subscription with a 14 day trial and the trial began three months ago, then you know the trial converted and is still active. If you are looking at a subscription with a 14 day trial and the subscription is only halfway through the trial, then you'll know the subscription is still in trial and just has not been canceled or had the chance to convert yet.