There appears to be multiple threads about that today. There seems to be a problem on Apple's end. You are going to have to wait until they get it fixed.
This thread has been closed by the system or the community team.
You may vote for any posts you find helpful, or search the Community for additional answers.
I can’t download apps on my iPhone
Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.