iPhone asks me to "Update Payment Details" but provides no way to do it
I just started getting a notification on my iPhone titled "Update Payment Details" that tells me, "There was a problem with your iCloud storage payment. Update your payment details to keep your 200 GB of iCloud storage." When I click on the "Update Payment" link below the message, it takes me to the "Payment & Shipping" screen. It shows my payment method (which is PayPal), but gives me no method for modifying anything. There is no indication on this last screen that there is any problem with the payment method.
I tried logging in to iCloud via a browser on my laptop and managing my Apple ID from there. There is nothing showing as wrong with my payment methods. I have received no emails or other notifications other than the one in my iPhone.
Does anyone know what is going on?
iPhone SE