There is a bug in the ORACLE client 18c.: https://support.oracle.com/knowledge/Oracle%20Database%20Products/2519112_1.html
The folllowing symbolic link is missing in $ORACLE_HOME/lib of the ORACLE-Client
lrwxrwxrwx 1 oracle oracle 12 Feb 28 06:28 libclntsh.so.12.1 -> libclntsh.so*
This link is necessary to ensure the compatibility with former ORACLE Versions.
Release : 12.3
Component :Automation Engine and DB utilities 12.3.
Create the missing symbolic link in $ORACLE_HOME/lib:
ln -s ibclntsh.so* libclntsh.so.12.1
If no access to this folder is given to the user, the DBA should be asked.