I no longer need a plug in on one domain and would like to move it to another. Am I required to purchase an additional license or is there a way to disconnect the purchase from one domain and install on another?
Please check your wp-admin plugin settings is there any deregister the license options? if you can find then you can deregister the license from the current website and register for the new website.
Also you can contact plugin author to get assist from them.
Otherwise you have to purchase a new license for the new website. Because each license will work only for a single end product.