Atlassian has posted the following relevant information regarding Atlassian Marketplace addons and development licenses of JIRA:
https://www.atlassian.com/licensing/marketplace#licensingandpricing-4


Which points to:
https://developer.atlassian.com/market/add-on-licensing-for-developers/licensing-and-paid-via-atlassian-listings

Go to the section titled, "Can customers use developer licenses for my add-on?" which has instructions on how to get a developer license for add-ons.

In summary: A
developer license can be generated (free of charge) once the plugin has been purchased and can only be installed on a development licensed version of JIRA.