Why doesn't the MathJax preview show when using ckeditor and Django?

I'm currently trying to create a simple website using Django, with ckeditor for form fields. I would also like to integrate some Mathematics into my forms, hence why I downloaded the Mathematical Formulas plugin for ckeditor.

I followed this tutorial to implement the plugin but MathJax doesn't work.

This is what I added to my settings.py file

CKEDITOR_CONFIGS = {
    'default': {
        'toolbar':'full',
        'height': '400px',
        'width': '100%',
        'extraPlugins': ','.join(
            [
                'mathjax', 
                'widget', 
                'lineutils', 
                'dialog', 
                'clipboard',
                
            ]),
    },

}

I copied the MathJax folder I downloaded into my project's static directory. I then refer to this in my models.py file:

from django.db import models
from django.contrib.auth.models import User
from ckeditor.fields import RichTextField

class Entry(models.Model):
    entry_title = models.CharField(max_length=100)
    #entry_text = models.TextField()
    entry_text = RichTextField(blank = True, null = True,config_name = 'default', external_plugin_resources=[(
        'mathjax',
        '/static/entries/vendor/ckeditor_plugins/mathjax/',
        'plugin.js',
    )])
    entry_date = models.DateTimeField(auto_now_add = True)
    entry_author = models.ForeignKey(User, on_delete = models.CASCADE)

    class Meta:
        verbose_name_plural = "entries"

    def __str__(self):
        return f'{self.entry_title}'

When I use my form, I can see the mathematical formulas symbol:

When I click on it, ckeditor gives me the freedom to type whatever I want into the Tex field:

However, it doesn't give me a preview of what it will look like after it has been rendered. This contradicts with the Mathematical Formula website, which gives an example of what it should look like:

Furthermore, when I click ok with my dummy Tex input, it doesn't show anything in the ckeditor box. This is followed by a message in my terminal Not Found: /create_entry/undefined and "GET /create_entry/undefined HTTP/1.1" 404 2644. 'create_entry' is a urlpattern I used when creating a form.

When I submit a form with some math in it, I cannot physically see the maths in the ckeditor field - only a blue cursor:

However, upon viewing this post after submission, the math renders:

I'm not sure if this is because I added this javascript in my base.html file:

    <script type="text/javascript" async
  src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_CHTML">
  </script>

Any help is appreciated, Thanks.

EDIT: I copied this code into my settings.py file and it works:

# CKEditor UI and plugins configuration
CKEDITOR_CONFIGS = {
    'default': {
        # Toolbar configuration
        # name - Toolbar name
        # items - The buttons enabled in the toolbar
        'toolbar_DefaultToolbarConfig': [
            {
                'name': 'basicstyles',
                'items': ['Bold', 'Italic', 'Underline', 'Strike', 'Subscript',
                          'Superscript', ],
            },
            {
                'name': 'clipboard',
                'items': ['Undo', 'Redo', ],
            },
            {
                'name': 'paragraph',
                'items': ['NumberedList', 'BulletedList', 'Outdent', 'Indent',
                          'HorizontalRule', 'JustifyLeft', 'JustifyCenter',
                          'JustifyRight', 'JustifyBlock', ],
            },
            {
                'name': 'format',
                'items': ['Format', ],
            },
            {
                'name': 'extra',
                'items': ['Link', 'Unlink', 'Blockquote', 'Image', 'Table',
                          'CodeSnippet', 'Mathjax', 'Embed', ],
            },
            {
                'name': 'source',
                'items': ['Maximize', 'Source', ],
            },
        ],

        # This hides the default title provided by CKEditor
        'title': False,

        # Use this toolbar
        'toolbar': 'DefaultToolbarConfig',

        # Which tags to allow in format tab
        'format_tags': 'p;h1;h2',

        # Remove these dialog tabs (semicolon separated dialog:tab)
        'removeDialogTabs': ';'.join([
            'image:advanced',
            'image:Link',
            'link:upload',
            'table:advanced',
            'tableProperties:advanced',
        ]),
        'linkShowTargetTab': False,
        'linkShowAdvancedTab': False,

        # CKEditor height and width settings
        'height': '250px',
        'width': 'auto',
        'forcePasteAsPlainText ': True,

        # Class used inside span to render mathematical formulae using latex
        'mathJaxClass': 'mathjax-latex',

        # Mathjax library link to be used to render mathematical formulae
        'mathJaxLib': 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS_SVG',

        # Tab = 4 spaces inside the editor
        'tabSpaces': 4,

        # Extra plugins to be used in the editor
        'extraPlugins': ','.join([
            # 'devtools',  # Shows a tooltip in dialog boxes for developers
            'mathjax',  # Used to render mathematical formulae
            'codesnippet',  # Used to add code snippets
            'image2',  # Loads new and better image dialog
            'embed',  # Used for embedding media (YouTube/Slideshare etc)
            'tableresize',  # Used to allow resizing of columns in tables
        ]),
    }
}

I found it on this website.