First if you're like me you're practically taking the photo with the phone pointed straight down. Pointing straight down or straight up are trouble for phones with auto rotate turned on because the device needs at least some tilt to know which way is up. You can disable auto rotate when performing this function in the quick settings above your notifications. If you have a Samsung device you could write a Bixby routine to do this for you when you open your banking app.
I am a bit confused about the not taking the picture statement. Do you mean that the app is not accepting the photos you're providing or do you mean that it won't capture the image? Could it be that it isn't accepting the image because it appears upside down because of your auto rotate? You'll have to provide a bit more information for help with this one.
Welcome to Android Central! Which phone do you have? Banking apps can be notoriously buggy, especially when it comes to interfacing with the camera. Send feedback to the app's developer.