Camera doesn't work in Payment & Shipping Settings

When my phone complains that I need to update my payment method for subscriptions and the like, and I follow the prompts to do so, I wind up in Payment & Shipping, where I can add payment methods but that isn't either the Wallet app nor Apple Pay. (WHY must there be THREE DIFFERENT PLACES to add payment methods to the iPhone???😖😖😖)

Anyway: when I tap the camera button to try to add a card using the camera in this mysterious third card-adding place, the camera frame is always entirely black, as if the camera is turned off altogether (and yet the camera works fine under all other circumstances). Anybody know why this is and how I fix it?

Thanks in advance...