iTunes Store is Unable to Process Purchases error over wifi?

I have an iPhone 6s running iOS 10.3.2. For the last few days, I haven't been able to update installed apps when connected to a wifi network. I just get an error saying "The iTunes Store is unable to process purchases at this time. Please try again later."

The error occurs when I am connected to any Wifi network (home and office, for example). Updates download fine if I turn off Wifi and use Verizon's data connection. I can, however, download new apps from the App Store on wifi.

Other iPhones and iPads have no trouble downloading updates on the same Wifi networks.

I have restarted my iPhone a few times. I have also logged out of the App store (Settings -> iTunes & App Store -> Tap on my Apple ID -> Sign Out). I have also logged completely out of iCloud. I have also reset network settings.

Can anyone shed some light on what might be going on?