Cannot get ssh working between ubuntu & centos machines

I am able to get SSH working between two UBUNTU machines however, I cannot copy an SSH ID between an UBUNTU 18.04 and CENTOS 7.6. I continuously get "Permission Denied". I have tried so many manual fixes and have been able to get nowhere. BTW, this is a PNET lab, not live equipment...

eve@server:~$ ssh-copy-id -i .ssh/id_rsa.pub centos7
eve@centos7's password:
Permission denied, please try again.

Any assistance would be greatly appreciated...