Appstore review: “Sign in with Apple” doesn’t work

[Nam Nguyen]

I made an iOS app using bitbucket api. Users will be directed to Bitbucket login website to log in. Its working well when i test it. 
But when Appstore reviewer tried to sign in with Apple account. It says "We're having trouble logging you in. There seems to be an issue with your identity provider. Wait a few moments, then try again."

so my app is denied. I don’t know what I can do about this because it’s Bitbucket website outside of my app, and it’s working fine when I test it myself. Any help is much appreciated 🙏

Here are the screenshots Apple reviewer sent me