ORA-12154 on newly created PDB when trying to connect with admin

@pdborcl3

I newly created a PDB using dbca interactively.

I created pdb_admin3/password and when trying to connect with SQLPLUS I'm getting
ORA-12154

I can connect to another PDB flawlessly using its pdb_admin/password@pdborcl for example.
But typing

sqlplus pdb_admin3/<weakpassword>@pdborcl3  (I must confess that I ignored the warning about creating a password not conforming to the complexity rules)

I'm getting this ORA-12154.

I also did an

ALTER PLUGGABLE DATABASE ALL OPEN

to no avail.

--

Christoph