Django can't get the parameters of the POST request?

when using axios to send a POST request to the backend, the server cannot get the parameters that are included in the POST.
the sending code of the front end is as follows:

Http({
    method:"POST",
    url:"signup",
    data:{
        username:this.signUpform.username,
        password:this.signUpform.password,
        email:this.signUpform.email,
        cellphone:this.signUpform.cellphone
    }
})

Axios settings are as follows:

import axios from "axios"
export default axios.create({
  baseURL: "http://127.0.0.1:8000/api",
  timeout: 20000,
  headers: {"Content-Type": "application/json"}
})

the backend acceptance code is as follows:

@require_http_methods(["POST"])
def signup(request):
    response = {}
    try:
        print(request.POST.get("username"))
        WorkUser.objects.get(username=request.POST.get("username"))
        response["error"] = "username already exist"
    except WorkUser.DoesNotExist:
        wu=tools.toWorkUser(request)
        wu.save()
        response["error"] = "success"
        
    return JsonResponse(response)

output, display:

None
Internal Server Error: /api/signup
Traceback (most recent call last):
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\datastructures.py", line 77, in __getitem__
    list_ = super().__getitem__(key)
KeyError: "username"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\exception.py", line 35, in inner
    response = get_response(request)
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\base.py", line 128, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\handlers\base.py", line 126, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\views\decorators\http.py", line 40, in inner
    return func(request, *args, **kwargs)
  File "E:\WorkSpace\GraduationThesis\GPServer\server\views.py", line 36, in signup
    WorkUser.objects.get(username=request.POST["username"])
  File "C:\Users\fengfanfan\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\datastructures.py", line 79, in __getitem__
    raise MultiValueDictKeyError(key)
django.utils.datastructures.MultiValueDictKeyError: "username"

however, you can use the Postman interface, which is why