DisallowedHost at /admin -- Django, Gunicorn, NGINX -- Error first showed when changed to HTTPS only instead of just HTTP

Question

This is a screenshot of the error when you access my domain, insa-analytics.com/admin:

Here is a text dump of that image for those who cannot access the image:

DisallowedHost at /admin
Invalid HTTP_HOST header: 'insa-analytics.com'. You may need to add 'insa-analytics.com' to ALLOWED_HOSTS.
Request Method: GET
Request URL:    http://insa-analytics.com/admin
Django Version: 4.0.2
Exception Type: DisallowedHost
Exception Value:    
Invalid HTTP_HOST header: 'insa-analytics.com'. You may need to add 'insa-analytics.com' to ALLOWED_HOSTS.
Exception Location: /usr/local/lib/python3.8/dist-packages/django/http/request.py, line 135, in get_host
Python Executable:  /usr/bin/python3
Python Version: 3.8.10
Python Path:    
['/home/django/django_project',
 '/usr/bin',
 '/usr/lib/python38.zip',
 '/usr/lib/python3.8',
 '/usr/lib/python3.8/lib-dynload',
 '/usr/local/lib/python3.8/dist-packages',
 '/usr/lib/python3/dist-packages']
Server time:    Mon, 18 Apr 2022 22:33:43 +0000

The /admin is the administrator control panel for the Django service. Previously, this webserver was working perfectly via HTTP (no SSL, 80 instead of 443). When I used certbot with letsencrypt to generate and configure an SSL certificate -- this issue came into play.

Note that I redirect all HTTP connections to HTTPS. My webservice will be only accessible over 443.

settings.py:

"""
Django settings for django_project project.

Generated by 'django-admin startproject' using Django 2.2.12.

For more information on this file, see
https://docs.djangoproject.com/en/2.2/topics/settings/

For the full list of settings and their values, see
https://docs.djangoproject.com/en/2.2/ref/settings/
"""

import os
import netifaces

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))


# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/2.2/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = OMITTED_FOR_STACK_OVERFLOW_QUESTION

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = False

# Find out what the IP addresses are at run time
# This is necessary because otherwise Gunicorn will reject the connections
def ip_addresses():
    ip_list = []
    for interface in netifaces.interfaces():
        addrs = netifaces.ifaddresses(interface)
        for x in (netifaces.AF_INET, netifaces.AF_INET6):
            if x in addrs:
                ip_list.append(addrs[x][0]['addr'])
    return ip_list

ALLOWED_HOSTS = ip_addresses()
ALLOWED_HOSTS += ['insa-analytics.com']


# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

ROOT_URLCONF = 'django_project.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'django_project.wsgi.application'


# Database
# https://docs.djangoproject.com/en/2.2/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'django',
        'USER': 'django',
        'PASSWORD': 'e1ceb12e126563cc2b5fa8a91f318db9',
        'HOST': 'localhost',
        'PORT': '',
    }
}


# Password validation
# https://docs.djangoproject.com/en/2.2/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]


# Internationalization
# https://docs.djangoproject.com/en/2.2/topics/i18n/

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/2.2/howto/static-files/

STATIC_URL = '/static/'

nginx server block cfg:

upstream app_server {
    server unix:/home/django/gunicorn.socket fail_timeout=0;
}

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /usr/share/nginx/html;
    index index.html index.htm;

    client_max_body_size 4G;
    server_name _;

    keepalive_timeout 5;

    # Your Django project's media files - amend as required
    location /media  {
        alias /home/django/django_project/django_project/media;
    }

    # your Django project's static files - amend as required
    location /static {
        alias /home/django/django_project/django_project/static;
    }

    # Proxy the static assests for the Django Admin panel
    location /static/admin {
       alias /usr/lib/python3/dist-packages/django/contrib/admin/static/admin/;
    }

    location / {
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $host;
            proxy_redirect off;
            proxy_buffering off;

            proxy_pass http://app_server;
    }

}


server {

    root /usr/share/nginx/html;
    index index.html index.htm;

    client_max_body_size 4G;
    server_name insa-analytics.com; # managed by Certbot

    keepalive_timeout 5;

    # Your Django project's media files - amend as required
    location /media  {
        alias /home/django/django_project/django_project/media;
    }

    # your Django project's static files - amend as required
    location /static {
        alias /home/django/django_project/django_project/static;
    }

    # Proxy the static assests for the Django Admin panel
    location /static/admin {
       alias /usr/lib/python3/dist-packages/django/contrib/admin/static/admin/;
    }

    location / {
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $host;
            proxy_redirect off;
            proxy_buffering off;

            proxy_pass http://app_server;
    }



    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/insa-analytics.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/insa-analytics.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot


}

server {
    server_name www.insa-analytics.com;
    return 301 $scheme://insa-analytics.com$request_uri;


    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/insa-analytics.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/insa-analytics.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
    if ($host = insa-analytics.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    listen 80 ;
    listen [::]:80  ;
    server_name insa-analytics.com;
    return 404; # managed by Certbot


}


server {
    if ($host = www.insa-analytics.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    server_name www.insa-analytics.com;
    listen 80;
    return 404; # managed by Certbot


}