pg_rewind: ERROR: could not fetch remote file "global/pg_control": ERROR: permission denied

I came across this error by using repmgr5.4 for pg15, but the problem arose
in pg_rewind, so I installed pg16 and tried again, the error persists like
this:

$ /usr/pgsql-16/bin/pg_rewind -D '/pgdata' --source-server='host=172.17.1.2
port=5432 user=rep dbname=repmgr connect_timeout=5'
pg_rewind: error: could not fetch remote file "global/pg_control": ERROR:
permission denied for function pg_read_binary_fileOriginally the server
here at 172.17.0.2 was the primary and 172.17.1.2 was the standby
replication server. I have created the user 'rep' with full replication
privilege as described on page:
https://www.postgresql.org/docs/16/app-pgrewind.html

CREATE EXTENSION repmgr;
GRANT pg_checkpoint TO rep;
GRANT pg_read_all_stats TO rep;
GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text, boolean, boolean) TO rep;
GRANT EXECUTE ON function pg_catalog.pg_stat_file(text, boolean) TO rep;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text) TO rep;
GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint,
bigint, boolean

And I have made it 'trust' among the intranet 172.17.0.0/16 in pg_hba.conf:

#host all all 127.0.0.1/32 ident

#host replication all 127.0.0.1/32 ident

host all rep 172.17.0.0/16 trust

host all postgres 172.17.0.0/16 trust

I have also made changes in postgresql.conf:

#wal_level = 'replica'

#full_page_writes = on

wal_log_hints = on

synchronous_standby_names = '*'

I used repmgr -h 172.17.0.2 -U rep -d repmgr standby clone to make the
replica/standby on 172.17.1.2 and basically it called pg_basebackup to do
the job. Checking the replication status from the old primary @172.17.0.2
with

SELECT * FROM pg_stat_replication;
would return a table containing:
state=streaming, sync_state=async

After that, I shut down the postgresql server on the old primary. And
ordered `pg_ctl -w -D '/pgdata' promote` to turn it into the new primary.

After that is where the issue occured - the pg_rewind on the old primary
won't function and threw out the error code.