The fastest and the easiest way to share your digital card is by using the widget. If it’s saved to the "Today" screen of your iPhone (the one you can access by swiping left on the lock screen), you can share your card even when your iPhone is locked!
Here is how to add the widget:
Long-press on your home screen until the app icons jiggle
Tap "Edit" at the top-left corner
Search "Haystack"
Choose your widget size and tap "Add widget"