I have just tested kali-linux-2020.1b-live-amd64.iso and username "kali" and password "kali" work without problems.

1) Is this on a live image?
2) If it's not and you proceeded with your installation, did you change the default username/password during installation?

Your comment didn't show up for some reason. In that case, it seems like you might have changed the default username and/or password during installation.
Try logging in with the username kali and a blank password to your installed distro. (Or the username/password you assigned during installation if you remember making that change)
If it works, sudo passwd kali and set a new password for it
If it doesn't, you might wanna reinstall on a VM and try reproducing the issue (leaving the default username as kali along with the password kali)

This is a bug tracker, not a support forum. Please ask for help on forums.kali.org or on IRC. Thank you.