The plugin has a feature to automatically create and send discount coupons to customers who left a review. If you enabled this feature (on Review for Discount tab in the plugin's settings) but the plugin doesn't create create new coupons after customers submit reviews, you should check how these reviews were created.
Review for Discount feature of the plugin works only for reviews that were submitted via aggregated review forms (What is an Aggregated Review Form?). If customers submitted reviews directly on WooCommerce product pages, the plugin will not be able to trigger creation and sending of discount coupons.
You can easily check if a review was submitted via an aggregated review form. To do that, go to WordPress admin area and then navigate to Reviews page (in the plugin's menu) where you should see a list of reviews. If a review has "via CR" label, it means that it was submitted via an aggregated review form.