Follow the step-by-step guide to activate the Goog Integration in the MARA Help Center. Make sure you log in with a Google user that has admin/owner permissions for the respective property, and eventually try a different user for the Google login.
If an active Google Integration stops working, first verify that the review still exists on Google and has not been deleted.
If you cannot see the "send" button for multiple existing reviews, the rights in your account/your integration might have changed. Contact the MARA support and include information about the property name, a screenshot of a review that you cannot reply to anymore.