I am creating a django rest API(with a ImageField) and it is working fine. But I want to add some validations to some CharFields fields. I noticed some unicodeDecoderError while added a validator or simply raising a validation error. Spent quite a lot of time trying to solve it. Any help will be appreciated.

Here is my serializers.py file

from rest_framework import serializers
from .models import *

def validate_phone(phone_number: str):
  print(phone_number)
  if not (phone_number.startswith(("6", "7", "8", "9"))):
    raise serializers.ValidationError(
        {"phone": "phone number must startwith digits from 6-9 !!!"})

  if not phone_number.isnumeric():
    raise serializers.ValidationError(
         {"phone": "phone number should contain digits only !!!"})

  if len(phone_number) != 10:
     raise serializers.ValidationError(
         {"phone": "phone number must contain only 10 digits !!!"})


class StudentSerializer(serializers.ModelSerializer):
  start_date = serializers.DateField(format='%d %B %Y')
  phone = serializers.CharField(max_length=10, validators=[validate_phone])
  class Meta:
    model = Student
    fields = '__all__'

Raising a validation error is resulting a UnicodeDecoderError. Working fine otherwise.

This is my models.py file

from django.db import models

class Student(models.Model):
    ...
    phone = models.CharField(max_length=10)
    ...
    start_date = models.DateField()
    profile_picture = models.ImageField(upload_to='profile/', blank=True)
    ...

I am sending the data using javascript fetch API with FormData() which handles the file formatting and encoding.

Here is the javascript file:

const form = document.querySelector("form");
form.addEventListener("submit", (e) => {
  e.preventDefault();

  const formdata = new FormData(form);
  const json_data = Object.fromEntries(formdata);
  console.log(json_data);

  const requestOptions = {
    method: 'POST',
    body: formdata,
  };

  fetch("http://127.0.0.1:8000/api/join/", requestOptions)
    .then((response) => response.json())
    .then((result) => console.log(result))
    .catch((error) => console.error(error))

Feeling helpless. Without raising a ValidationError it is working fine, I just want to add some validations without any UnicodeDecodeError. I tried to test with postman and the result is same. I do not know how to proceed.

Where am I missing