The error received was:
ERROR: Unable to install the “psa-9.3.0-cos5.build93091230.06.x86_64″ package
Not all packages were installed. Please, contact product technical support.
Not a very useful error message as it tells us nothing about the problem. In previous versions of Plesk on Redhat based operating systems it was the upgraded bind-libs causing the Plesk install to fail. Same in this case.
RUN:
rpm -e bind-libs bind-utils
And re-install Plesk 9.3 from scratch.