You have successfully run installation part of WebAccess and want to continue with configuration section but that fails with python scripting errors.
One of the requirements for successful installation of WebAccess is to have python2 extension enabled on SLES15 extensions. However, this does not supply all necessary python RPMs.
Make sure, that prior installing WebAccess or WebPublisher, you run those two commands from a server terminal window:
zypper in python2-rpm
zypper in python-xml
Although in most cases python2-rpm is installed by enabling python2 extensions, the other, python-xml, is not and that part is a cause of getting python script errors during configuration part of WebAccess installation.
Be aware of this information referred to in the "Resolution" section of this document, "readme file",
OS Support Changes: