Reclaim requires the Jira issue to have:
a due date and/or fix version and/or Sprint, and
be assigned to a user with an email registered in Reclaim who has the integration enabled.
A Jira issue that does not have all the required fields Reclaim needs in order to sync it will show what is needed for the sync to work:
The Schedule via Reclaim button will sync the issue to Reclaim to start blocking time for the Task on your calendar.
A Jira issue that has a sync to Reclaim will show:
A link to the associated Task in Reclaim.
The Task's first scheduled event.
Note: sometimes you'll need to refresh your browser in order to see updated states on your Jira issues.