Thank you for reaching out to us. We would love to help you out with this. Could you please provide us little more information?
OS version?
Application Version?
Make and model of device?
Is camera working with other apps?
Worflow which you are following?
When you open your Scan app in capture mode, it asks you to allow access to the camera. If you do not allow access from the app, you can go to your device settings to allow access, which you said you did. In settings, go toAdobe Scanand you should see a 'Camera' toggle button. You need to tap the button to slide it green. Once you do that, you can open the Scan app to capture your document.
You may try an alternate way to allow camera access: Go to Settings > Privacy > Camera. All the app that requested camera access will be listed there. If you see Adobe Scan option, tap the toggle button to enable it. Hope it helps!
Let us know if you somehow do not see the Camera toggle button.
If possible do share some relevant screenshots with us. Once we've got that information from you, we can take a closer look.