No sound on iPhone for push notifications
Can't find a setting to get sound on these notifications.
At the moment our iOS app does not have any extra settings. The push notification sounds should be your default sound for notifications on your iOS device.
Also please make sure that you allow the Todoist app to generate notifications in your phone's settings, and that your phone is listed on the list of devices in Todoist's Settings -> Reminders (on the web-app, todoist.com)