Hi Steve,
Sorry to hear you're having trouble with this! Your best bet for getting this resolved is to contact
sup...@stripe.com directly so that someone can have a look at your account. In general, these are the steps for renewing your Apple Pay iOS certificate:
1. Go to Payments -> Apple Pay in the Stripe Dashboard
2. Click "Add new application"
3. Download the CSR from Stripe.
4. Create the new certificate in your Apple Developer dashboard & download it.
5. Upload the new certificate using the prompt in the Stripe Dashboard.
It sounds like something is blocking you at step 3, which is very odd—nothing has recently changed there, and I'm able to go through the above flow on my own account without issue. What I'd recommend for a quick resolution is using this contact form to write in so that your account ownership is verified when you contact support:
I also wanted to note that, for future renewals, you can create and upload the new certificate before your renewal date. Once you've generated & uploaded the new certificate it only takes a few minutes for your deployed applications to start using the updated cert.
Sorry I don't have an easy resolution here! Support should be able to get this sorted out for you quickly.