This might be caused when photos have not finished uploading and so you can’t place the order in the app. To ensure your photos upload onto our service, follow these steps:
Make sure you’re connected to a reliable Wi-Fi network.
Make sure you have the latest version of the app installed. You can confirm this by going to the Apple Store or Google Play store and see if you have the latest version.
Sign out and sign back in.
Force quit the app and open it again.
Open the app and leave it open, preferably overnight (do not back out of the app or close it).