"render_placeholder" Not Showing Up In Djangocms Template

I have followed the instructions on the following site in order to render a placeholder field from a model, but I didn't manage. http://docs.django-cms.org/en/release-3.4.x/how_to/

Solution 1:

You are missing the PlaceholderAdminMixin on the admin I think. You did not specify the admin so I am not sure.

from django.contrib import admin
from cms.admin.placeholderadmin import PlaceholderAdminMixin

class HomePageAdmin(PlaceholderAdminMixin, admin.ModelAdmin):
    pass