// build issue input
final String summary = "Some subtask";
final String description = "Some description for substask";
// prepare IssueInput
final IssueInputBuilder issueInputBuilder = new IssueInputBuilder(project, issueType, summary)
.setDescription(description)
.setFieldValue("parent", ComplexIssueInputFieldValue.with("key", issue.getKey()));
// create
final BasicIssue basicCreatedIssue = issueClient.createIssue(issueInputBuilder.build()).claim();
assertNotNull(basicCreatedIssue.getKey());
return basicCreatedIssue;
}