Sign up with Apple not working

I have implemented a Sign up with Apple button with usePopup=true. When I click the button I get the popup window. After authenticating I click the final "Continue" button and nothing happens. Well technically there is a request to https://appleid.apple.com/appleauth/auth/oauth/authorize. Clicking "Continue" more than once results in the error "Your request could not be completed because of an error. Please try again later." Where do I go from here?