setting up streaming replication

I'm stumped.

Using this command to set up the slave and replication on PG v 15:
"C:\Program Files\PostgreSQL\15\bin\pg_basebackup" -h 192.168.1.126 -U
pgrep_user -p 5433 -D "C:\Program Files\PostgreSQL\15\data" -Fp -Xs -R

If I have PG running on the remote server and the data directory is intact,
then I get an error, Data exists and is not empty.

If I shut down PG, delete data\*, restart PG, then it fails to start
because the conf files are missing.

If I leave PG shut down and run pg_basebackup, it times out and asks if pg
is running and listening on the port. Of course it is not.

I see lots of posts on how to use pg_basebackup, but apparently this isn't
interesting because no one mentions whether pg should be running on
the remote server. Just that the data dir must be empty.

I know this works because I've done it before. But I don't see the trick
I'm missing.

Thanks,
Brad.