REACT call (Post) to Api (Laravel) return error 500

I am fairly new to web developing and i am currently practicing with laravel and react.

At the moment i have a problem with a api call (post) getting back an error 500.

Here is the php code:

Model

protected $fillable = [
    'id',
    'name',
    'address',
    'phone',
    'email'

Controller

public function store(Request $request)
{
    $customer = Customer::create($request->all());
    return response()->json($customer, 201);
}

Api route

Route::apiResource('customers', 'App\Http\Controllers\CustomerController');

Here is the js code:

service (customers.js)

  export async function addCustomer(customer) 
  {
    fetch( '/api/customers/', 
    {
      method:'post',
      headers: 
      {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(customer)
    })
    .then(response => 
    {
      console.log(response);
      return response.json();
    })
  }

component (CustomerForm.js)

const CustomerForm = ({customer, showForm}) => {
    [...]
    const handleSubmit = (e) => 
        {
        e.preventDefault(); 
        addCustomer(model)
        .then(i => {}, 
            error => 
              {
              console.log(error.message)
              })
        .catch(e => 
          {
          console.log(e)
          console.log(response)
          }); 
         }

    /**
     * render
     */
    return (
        [...]
    );
}

export default CustomerForm;

Here is the error:

POST http://127.0.0.1:8000/api/customers/ 500 (Internal Server Error)
_callee3$   @   app.js:6606
tryCatch    @   app.js:6524
(anonymous) @   app.js:6524
(anonymous) @   app.js:6524
asyncGeneratorStep  @   app.js:6526
_next   @   app.js:6528
(anonymous) @   app.js:6528
(anonymous) @   app.js:6528
_addCustomer    @   app.js:6625
addCustomer @   app.js:6594
handleSubmit    @   app.js:5704
onSubmit    @   app.js:5725
[...]

What I've done:

• The same call works fine with postman.
• There is the csrf-token in my html head.

Any suggestion?