If you see the error bellow it means that you haven’t configured the mod_plsql PlsqlDatabaseConnectString parameter correctly in dads.conf. There are multiple ways to configure it:
1. Connection string:
2. TNSName entry with tnsnames.ora
For this to work you also need to have a tnsnames.ora file in OHS_HOME/network/admin/tnsnames.ora (in my case /u01/app/oracle/product/FMW/Oracle_WT/network/admin/tnsnames.ora) with the corresponding tns entry.
3. TNSNameFormat (Notice there are no spaces)
With this you can put multiple servers, create load balance, etc. as you would do with a tns entry in tnsnames.ora file.