unable to import rest_framework - django

Question

I have Anaconda installed in my system but clearly I have set up a new and clean environment for a django API project. I also have all the necessary requirements installed for the API. But when I try to import rest_framework it gives me an error saying "Unable to import 'rest_framework' " even when I have done the following:
#settings.py
INSTALLED_APPS = [
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'rest_framework',
'api',
]
#serializers.py
from rest_framework import serializers #<---- this line is giving me error
from .models import Plans
class PlansSerializer(serializers.ModelSerializer):
"""Serializer to map the Model instance into JSON format."""
class Meta:
"""Meta class to map serializer's fields with the model fields."""
model = Plans
fields = ('id', 'name', 'date_created', 'date_modified')
read_only_fields = ('date_created', 'date_modified')
requirements.txt
certifi==2018.11.29
Django==2.1.7
django-crispy-forms==1.7.2
django-filter==2.1.0
django-markdown==0.8.4
django-markdown2==0.3.1
django-pagedown==1.0.6
djangorestframework==3.9.2
djangorestframework-simplejwt==4.1.0
Markdown==3.0.1
markdown2==2.3.7
olefile==0.46
Pillow==5.4.1
Pygments==2.3.1
PyJWT==1.7.1
pytz==2018.9
I also always deactivate the conda's base environment and only activate the required environment.