django.template.exceptions.TemplateSyntaxError: 'my_filter' is not a registered tag library. Must be one of:

This error message indicates that Django is unable to find the tag library for a custom filter called 'my_filter'. In order to use a custom filter in Django templates, you need to register it with the template engine using the 'register' decorator.

Here is an example of how to register a custom filter in Django:

from django import template

register = template.Library()

@register.filter(name='my_filter')
def my_filter(value):
    # your filter logic here
    return filtered_value

Make sure that the file containing the above code is included in your Django app's 'INSTALLED_APPS' setting, and that the filter is being called correctly in your template.