The plugin license will allow the plugin to work on sites on a multi-site installation. However, do not activate the plugin for all sites, but instead activate each site individually. You can order more sites or change your form count to the site count.
For instance, if you need 5 sites to use the plugin and you ordered the 1-SITE | 10-FORMS version, you can request 4 of the forms to be moved to the site count, changing your plan to 5-SITES | 6-FORMS.
Let us know if the above helps the issue you are having, or if more assistance is needed we remain at your service.