EXM uses a double opt-in process, so a contact will not be subscribed to a list before confirming subscription, see The EXM double opt-in process. In short:
- Contact subscribes to a list using the EXM ClientAPI
- An email which contains a link to confirm the subscription, is sent to the contact
- Contact clicks the link and is added to the list
As the contact is being created, and (I'm assuming) you're not seeing any errors, I believe you simply need to confirm the subscription, after which you will see the contact in the list.
In addition to this, I recommend that you disable list locking. If you don't, you are very likely to see problems when contacts subscribe/unsubscribe. To do so, you simply need to enable the following configuration file on your CM instance:
More details about list locking can be found in the release notes for 8.2 update 2