Postgresql 13 on CentOS8 fail to start at boot time, but can be started manualy

I have the following problem with postgres 13 on CentOS8.
It is installed on a separate disk mounted on /opt/pgsql/data (with the pg_wall mounted also on a separate disk – /opt/pgsql/wall) and at boot time fails to start, but if I run systemctl start postgresql-13 is starting fine.

After the reboot, checking the postgres service status I get the following error:

● postgresql-13.service - PostgreSQL 13 database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql-13.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2020-11-16 22:50:55 EET; 32s ago
     Docs: https://www.postgresql.org/docs/13/static/
  Process: 1203 ExecStart=/usr/pgsql-13/bin/postmaster -D ${PGDATA} (code=exited, status=1/FAILURE)
  Process: 1179 ExecStartPre=/usr/pgsql-13/bin/postgresql-13-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
 Main PID: 1203 (code=exited, status=1/FAILURE)

Nov 16 22:50:55 srvpsql systemd[1]: Starting PostgreSQL 13 database server...
Nov 16 22:50:55 srvpsql postmaster[1203]: 2020-11-16 22:50:55.928 EET [1203] LOG:  redirecting log output to logging collector process
Nov 16 22:50:55 srvpsql postmaster[1203]: 2020-11-16 22:50:55.928 EET [1203] HINT:  Future log output will appear in directory "log".
Nov 16 22:50:55 srvpsql systemd[1]: postgresql-13.service: Main process exited, code=exited, status=1/FAILURE
Nov 16 22:50:55 srvpsql systemd[1]: postgresql-13.service: Killing process 1214 (postmaster) with signal SIGKILL.
Nov 16 22:50:55 srvpsql systemd[1]: postgresql-13.service: Failed with result 'exit-code'.
Nov 16 22:50:55 srvpsql systemd[1]: Failed to start PostgreSQL 13 database server.

The service file in /etc/systemd/system/multi-user.target.wants has the following content:

[Unit]
Description=PostgreSQL 13 database server
Documentation=https://www.postgresql.org/docs/13/static/
After=opt-pgsql-wall.mount
After=syslog.target
After=network.target

[Service]
Type=notify
User=postgres
Group=postgres
Environment=PGDATA=/opt/pgsql/data/
OOMScoreAdjust=-1000
Environment=PG_OOM_ADJUST_FILE=/proc/self/oom_score_adj
Environment=PG_OOM_ADJUST_VALUE=0

ExecStartPre=/usr/pgsql-13/bin/postgresql-13-check-db-dir ${PGDATA}
ExecStart=/usr/pgsql-13/bin/postmaster -D ${PGDATA}
ExecReload=/bin/kill -HUP $MAINPID
KillMode=mixed
KillSignal=SIGINT


# Do not set any timeout value, so that systemd will not kill postmaster
# during crash recovery.
TimeoutSec=0

[Install]
WantedBy=multi-user.target

I've added opt-pgsql-wall.mount because I suspect that the postgres process is started before the mounting of the disk is done (it seems that wasn;t the cause of the error).

Also in postgresql.conf file (in /opt/pgsql/data folder) I have the current folder as data directory set.

...
data_directory = '/opt/pgsql/data/' 
...

What am I doing wrong ?