Structure plugin automatically installs a free license in case your JIRA runs on one of the following free licenses:

• Free license for open-source projects;
• Free license for a non-profit organization;
• Free community license;
• Free demonstration license;
• Free developer license.

The clauses from the Atlassian EULA that govern the use of those free licenses also apply to using Structure on JIRA servers where these licenses are installed.