Select the merchant ID to add to this certificate, click 'Create Certificate' in the Apple Pay Payment Processing Certificate section (on Apple).
File gets downloaded automatically.
When prompted to upload a certificate signing request, select the .certSigningRequest file you have downloaded and proceed to download.
Verify that the details of the certificate are correct, and download the certificate locally.
Upload the new certificate file on Stripe.
Go back to Apple’s Developer Center, select the MerchantID and activate the Apple Pay Payment Processing Certificate (Apple Pay settlement processing certificate) you created.