Accumulating Packages in Transit not working

[deep pelican]

Hi there 🙂 I'm kinda new to HA, so please bear with me.
I recently installed "Mail and Packages" and I'm trying to get an accumulated count of the packages.
In the documentation of Mail and Packages I found examples for cards. (https://github.com/moralmunky/Home-Assistant-Mail-And-Packages/wiki/USPS-Informed-Delivery-Image)

I tried using one of them, but "sensor.mail_packages_in_transit" is not working for me. Any idea here? Do I need to create that myself and if yes, how so? Thank you so much in advance and I'm happy to be here! 🙂

The code I have:

cards:

• cards: null
  entities:
  • entity: sensor.mail_packages_in_transit
    name: Todays Package Delivery
    type: entities
• cards: null
  entities:
  • entity: sensor.mail_dhl_delivering
    icon: 'mdi:package-variant-closed'
    name: DHL
  • entity: sensor.mail_hermes_delivering
    icon: 'mdi:package-variant-closed'
    name: Hermes
  • entity: sensor.mail_amazon_packages
    icon: 'mdi:package-variant-closed'
    name: Amazon
    show_header_toggle: false
    type: glance
• cards: null
  entities:
  • entity: sensor.mail_updated
    type: entities
    title: Mail & Package Tracking
    type: 'custom:vertical-stack-in-card'