Hello dmgriffin,
Thanks for reaching out to Apple Support Communities. We see you have some questions about using your iPhone to scan barcodes and QR codes with third party applications, and we'd like to help. Do you have permissions granted for your Camera application with these third party apps? The following link can help explain more about this, and how to do so: Control access to information in apps on iPhone - Apple Support
Review or change access to information in apps
The first time an app wants to use information from another app, you receive a request with an explanation. For example, a messaging app may request access to your contacts to find friends who are using the same app. After you grant or deny access, you can change access later.
1. Go to Settings > Privacy & Security.
2. Tap a category of information, such as Calendars, Reminders, or Motion & Fitness.
The list shows the apps that requested access. You can turn access on or off for any app on the list.
Also, we'd recommend restarting your device, to see if this helps with what you're seeing, as this can sometimes help with application issues on your device: Restart your iPhone - Apple Support
How to restart your iPhone X, 11, 12, 13, or later
1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
Also, to ensure your device has the most recent settings, we'd recommend updating your device, if needed. You can find assistance with that, here: Update your iPhone or iPad - Apple Support
Update your iPhone or iPad wirelessly
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.
Let us know if this helps.
Regards.