When debugging an app issue, logs are very helpful. Enable logs in both places below, then try your app again, and check the logs. You may need to refresh the log page to see new logs.
On your WordPress site
Visit the AppPresser settings on your WordPress site, and go to the Logs tab. Click enable logging.
Here you will be able to see logs when there is a new purchase or cancellation.
Visit your app dashboard, click your app, then the logs tab. Click enable logging, and the visit the app customizer Build and Preview tab and click Publish Changes. You must press Publish Changes or the logs will not work.