You can get ” ORA-12545 connect failed because target host or object does not exist ” error when connect to database via Toad or PLSQL Developer.
If you got ORA-12545 connect failed because target host or object does not exist error, probably you used hostname or scan name instead of Public IP adress or Scan IP.
You can try in CMD using nslookup if your client will resolve hostname or not
nslookup hostname nslookup SCAN-NAME
To solve this problem you need to change DNS Server and use same dns server with database server.
If you don’t change dns server then you should use Public IP or SCAN IP instead of hostname, SCAN Name.