Laravel api using in react spa.

my controller

<?php

namespace App\Http\Controllers\Api;

use App\Http\Controllers\Controller;
use App\Http\Requests\Api\AuthenticationRequest;
use App\Models\User;
use Illuminate\Http\Request;

class AuthenticationController extends Controller
{
    public function store(AuthenticationRequest $request)
    {
        $attributes = [
            'name' => $request->name,
            'email' => $request->email,
            'password' => $request->password,
        ];

        $user = User::create($attributes);
        session()->flash('success', 'Account registered successful.');
        return response()->json([
            'message' => 'User created successfully',
            'user' => $user
        ], 201);
    }
}

my react form submission

function handleSubmit(e) {
  e.preventDefault(); 

  fetch("http://127.0.0.1:8000/api/register", {
    method: "POST",
     headers: {
       "Content-Type": "application/json",
     },
    body: JSON.stringify(form), 
  })
    .then((response) => {
      if (!response.ok) {
        throw new Error(`HTTP error! status: ${response.status}`);
      }
      return response.json();
    })
    .then((data) => {
      console.log("Success:", data);
      setSuccess(data.message);
    })
    .catch((error) => {
      console.error("Error during registration:", error);
      setError("Registration failed. Please try again."); 
    });
}

getting this error in console when submitting the form

Register.jsx:25 Fetch finished loading: POST "http://127.0.0.1:8000/api/register".
Register.jsx:43 Error during registration: SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON
Register.jsx:25 Fetch finished loading: GET "http://localhost:3000/".

What's I'm missing?