Hi there furphy2,
If you are having issues adding a boarding pass to Apple Wallet on your iPhone, first ensure you are following the steps outlined here to accomplish this: Add, use, and share boarding passes, tickets, and other passes in Apple Wallet
If you are following those steps and this continues to occur, next check for an update to the software of your iPhone. This installs feature improvements and bug fixes that can resolve unexpected behavior like this. These steps from Update your iPhone or iPad show how to back up and update:
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
Cheers!