I'd be inclined to ensure that users ords_public_user and ords_metadata exist in the database and that the ords_public_user password that you are using is correct.
I'd then be inclined to run
select * from ords_metadata.ords_version;
on your database.
If you don't get a meaningful result then I suspect that you did not fully install v3.
V3 differs from V2 in that RESTful services needs the ords_metatdata schema in the database. This is created as part of the configuration.
Did you complete the part of the configuration that asks for sys database credentials? If not, reset and rerun the config. That is, do what the message tells you but make sure that you supply the correct sys credentials.
You might also want to read Colm's answer to ORDS_METADATA & multiple listener versions
If this does not solve the issue then you really need to provide more details about what you are doing. And with what.
I am assuming that you installed v3 on a server where v2 is working fine but the v3 listener errors on start.