[Answered ]-Django rest api not accepting raw data

If you are using Django auth User model, then relationship between User and Groups is many to many. A user can belongs to more than one groups. So you should write a custom create method for your serializer if you want to work it for you with same payload. It will be something like this

from django.contrib.auth.models import Group
def create(self, validated_data):
     user = get_user_model().objects.create(
               email=validated_data.get('email'),
               first_name=validated_data.get('first_name'),
               last_name=validated_data.get('last_name')
            )
     user.set_password('password')
     g = Group.objects.get(id=validated_data.get('group')) 
     g.user_set.add(user)

You should set content type as json in postman.

You only need to post the data maybe like this,

{
    "password":"12345678",
    "email":"mymail@yopmail.com",
    "groups":[1],
    "first_name":"Arun",
    "last_name":"Joshi"
}

Couple things to keep in mind,

• Relation between User and Groups is ManyToMany. So, the serializer accepts the data as a list only. Either you may need to write a custom create method, like @M Hassan suggested, or you just need to post it as a list.

• Primary keys are integer fields, don’t post them as strings. If you do, make sure you write appropriate code for catching the same.

If you are using requests
set at your headers
content-type: application/json
Like this

headers= {'content-type':'application/json'}
data = {
"password":"12345678",
"email":"mymail@yopmail.com",
"groups":"1",
"first_name":"Arun",
"last_name":"Joshi"}
resp = requests.post(url, headers=headers, data=data)

For postman, just add headers like this

Check your project settings also:

REST_FRAMEWORK = {
'PAGE_SIZE': 10,
'DEFAULT_RENDERER_CLASSES': (
    'rest_framework.renderers.JSONRenderer',
    'rest_framework.renderers.BrowsableAPIRenderer',
)}

Check this also:

from rest_framework.parsers import JSONParser

class MyUserViewSet(viewsets.ModelViewSet):
    queryset = get_user_model().objects.all()
    serializer_class = UserSerializer 
    parser_classes = (JSONParser,)