APEX Installation ORA-01435 while running @apxconf
Oracle support doc 1970925.1 suggests that this is because you're trying to use the wrong version of script with the installed APEX version (e.g. 5.0 APEX installation but 5.1 scripts).

Ensure you're using the right version of scripts with the right APEX version.

Another reason this could happen, is if APEX isn't even installed.  Note that with 12.2 onwards, APEX isn't installed in the database by default.