As I'm also using Expo, I followed the following to start with and there was no redirect_uri used.
https://medium.com/appandflow/eli5-sign-in-with-apple-for-react-native-using-expo-sdk35-node-js-5210cdb94bd6
I tried with one and it didn't make a difference. Also, in Apple's documentation, it doesn't show redirect_uri as being required.
https://developer.apple.com/documentation/signinwithapplerestapi/generate_and_validate_tokens
https://medium.com/appandflow/eli5-sign-in-with-apple-for-react-native-using-expo-sdk35-node-js-5210cdb94bd6
I tried with one and it didn't make a difference. Also, in Apple's documentation, it doesn't show redirect_uri as being required.
https://developer.apple.com/documentation/signinwithapplerestapi/generate_and_validate_tokens