If your app requires a login and you didn't include demo credentials in the review notes, Apple's reviewer hit a wall. This is one of the most common — and most fixable — rejections out there.
What Apple said
“We were unable to review your app, as your app requires a login but you have not provided us with demo account credentials in App Store Connect. Please provide a full-access account so we can review all features of your app.”
Apple's reviewers need to actually use your app. If it's behind a login screen and you didn't give them credentials, they can't evaluate it — so they reject it. This isn't a judgment on your app's quality, it's purely a process issue. The good news: it's completely fixable in your next submission.
While you're at it — Apple also requires these pages for every app.
Fix this rejection, then make sure you're covered on the compliance side too. Apple requires every app to link to a hosted Privacy Policy, Terms of Service, Support page, and Data Deletion page. No link means another rejection — just for a different reason.