If you don't have access to all of the photos you want to use as a background for the countdown, here's the solution to your problem:
Since updating to iOS14, you haven't given The Big Day access to all of your photos when the app asked you (which happens pretty quickly, so not your fault ;-)). This means you won't see all of the folders and / or photos when you try to add a photo to the countdown or as a profile picture.
You can fix it by following the steps below:
- Please go to your iPhone settings, scroll down until you see the The Big Day logo, and tap on it.
- There you will see alle permissions you have granted.
- Tap the "Photos" permission and change the setting to "All photos".
- Restart the app – now you should be able to see all photos in your gallery.