It appears to be:

mail0# /etc/rc.d/mlmmjadmin check                                                                                                                   
mlmmjadmin(ok)
mail0# ps -ax | grep mlmm
91673 ??  S        0:03.11 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja
81014 ??  I        0:00.03 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja
14371 ??  I        0:00.02 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja
49493 ??  I        0:00.04 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja
71941 ??  I        0:00.03 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja
9368 ??  I        0:00.03 /usr/local/bin/uwsgi --ini /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini --log-syslog --pidfile /var/run/mlmmjadmin/mlmmja

mail0# more /opt/mlmmjadmin/rc_scripts/uwsgi/openbsd.ini                                                                                           
[uwsgi]
master = true
vhost = true
enable-threads = true
processes = 5
logger = syslog:mlmmjadmin,local5
log-format = [%(addr)] %(method) %(uri) %(status) %(size) "%(referer)"

http-socket = 127.0.0.1:7790

# rc script will run program as mlmmj user, so no need to set uid/gid here.
#uid = mlmmj
#gid = mlmmj

chdir = /opt/mlmmjadmin
wsgi-file = mlmmjadmin.py
mail0# netstat -na | grep 779
tcp          0      0  127.0.0.1.7791         *.*                    LISTEN
tcp          0      0  127.0.0.1.7790         *.*                    LISTEN
tcp          0      0  127.0.0.1.7779         *.*                    LISTEN

Try this:

cd /opt/www/iredadmin/
python3 iredadmin.py

Any error?

This is the SQL debugging I see when I enable debugging on iredadmin. This is after the domain user list screen has been created when I click on a link to edit a user.

0.0 (1): SELECT * FROM sessions WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (2): SELECT * FROM sessions WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (3): UPDATE sessions SET atime = '2020-12-16T22:30:33.723669' WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.01 (1):
            SELECT
            mailbox.*,
            sbcc.bcc_address AS sender_bcc_address,
            sbcc.active AS sbcc_active,
            rbcc.bcc_address AS recipient_bcc_address,
            rbcc.active AS rbcc_active
            FROM mailbox
            LEFT JOIN sender_bcc_user AS sbcc ON (mailbox.username = sbcc.username)
            LEFT JOIN recipient_bcc_user AS rbcc ON (mailbox.username = rbcc.username)
            WHERE mailbox.username = 'redacted@domain.com'
            LIMIT 1

0.0 (2): SELECT address FROM forwardings WHERE forwarding='redacted@domain.com' AND is_list=1 GROUP BY address
0.0 (4): SELECT * FROM sessions WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (5): UPDATE sessions SET atime = '2020-12-16T22:30:33.748189', data = 'gASVFQI0A0AAAAB9lCiMCnNlc3Npb25faWSUjCg2NjczOWU2MTYxNmFlODY1NTQ2ZWM3MWQxMzgy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\nNnhTNzhCejM2NWtVUTRyNlVZODlmRDlXTWpSUJR1Lg==\n' WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
x.x.x.x:52264 - - [16/Dec/2020 22:30:33] "HTTP/1.1 GET /profile/user/general/redacted@domain.com" - 303 See Other
0.0 (1): SELECT * FROM sessions WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (2): SELECT * FROM sessions WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (3): UPDATE sessions SET atime = '2020-12-16T22:30:33.847091' WHERE session_id='66739e61616ae865546ec71d1382a9a449d9a302'
0.0 (1): SELECT COUNT(username) AS total FROM mailbox WHERE domain IN ('domain.com')

It ends by drawing the domain user list screen again. For safety in this post, I have altered the session id and session info.

Finally, a more detailed error message:

mail0# python3 maillist_admin.py create test-ml@domain.com
Traceback (most recent call last):
  File "maillist_admin.py", line 140, in <module>
    _json = r.json()
  File "/usr/local/lib/python3.8/site-packages/requests/models.py", line 897, in json
    return complexjson.loads(self.text, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/simplejson/__init__.py", line 525, in loads
    return _default_decoder.decode(s)
  File "/usr/local/lib/python3.8/site-packages/simplejson/decoder.py", line 370, in decode
    obj, end = self.raw_decode(s)
  File "/usr/local/lib/python3.8/site-packages/simplejson/decoder.py", line 400, in raw_decode
    return self.scan_once(s, idx=_w(s, idx).end())
simplejson.errors.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

mail0$ python3 -c "import web; print(web.__version__)"
0.61
mail0$ pkg_info | grep webpy                                                   
py3-webpy-0.61      web framework for python

Is it a locale issue perhaps?
mail0$ locale
LANG=
LC_COLLATE="C"
LC_CTYPE="C"
LC_MONETARY="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_MESSAGES="C"
LC_ALL=
mail0$