"Unprocessable Entity" passing data to Laravel controller via Ajax - ajax

Question

I'm trying to submit data to my Laravel Controller using Ajax, but I'm getting the error "422 (Unprocessable Entity)".
I've done some Googling, and I think it is to do with the JSON being passed, but I'm unsure how to solve it.
The following is what I believe to be the relevant info:
Script
$("#addStepNew").click(function() {
var step_ingredients = JSON.stringify(stepIngredients)
var step_description = $('#stepDescription').val();
var prep_step = $('input[name=prepStep]:checked').val();
$.ajax({
headers: {
'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
},
type: "post",
data: "ingredients="+step_ingredients+"&description="+step_description+"&is_prep="+prep_step+"step_no=1",
dataType:'json',
url: "{{ route('ingredients.store', ['id' => $recipe->id]) }}",
success:function(data){
console.log(data);
$("#output").html('<div class="alert alert-success my-0">'+data.name+' added</div>');
$("#output").toggleClass("invisible")
$("#output").fadeOut(2000);
}
});
});
The console.log(stepIngredients) gives [{"ingredient_id":"9","ingredient_quantity":"3","Ingredient_units":"kilograms"}]
The idea is to pass it all through to my controller, and write the values to the DB, but at the minute I can't even pass the info.
I've done the following to my controller:
public function store(Request $request)
{
//$this->validate($request);
/*
$step = new Step;
$step->recipe_id = $request->recipe_id;
$step->step_no = $request->step_no;
$step->method = $request->description;
$step->save();
*/
$data = [
'success' => true,
'message'=> 'Your AJAX processed correctly',
] ;
return response()->json($data);
}
So as I understand it (I'm teaching myself this as I go along), if the AJAX is passed successfully, then it should return the success message and output it in my #output div?
+--------+-----------+--------------------------+--------------------+------------------------------------------------------------------------+--------------+
| Domain | Method | URI | Name | Action | Middleware |
+--------+-----------+--------------------------+--------------------+------------------------------------------------------------------------+--------------+
| | GET|HEAD | / | | App\Http\Controllers\PagesController#index | web |
| | GET|HEAD | api/user | | Closure | api,auth:api |
| | GET|HEAD | home | home | App\Http\Controllers\HomeController#index | web,auth |
| | GET|HEAD | login | login | App\Http\Controllers\Auth\LoginController#showLoginForm | web,guest |
| | POST | login | | App\Http\Controllers\Auth\LoginController#login | web,guest |
| | POST | logout | logout | App\Http\Controllers\Auth\LoginController#logout | web |
| | POST | password/email | password.email | App\Http\Controllers\Auth\ForgotPasswordController#sendResetLinkEmail | web,guest |
| | GET|HEAD | password/reset | password.request | App\Http\Controllers\Auth\ForgotPasswordController#showLinkRequestForm | web,guest |
| | POST | password/reset | | App\Http\Controllers\Auth\ResetPasswordController#reset | web,guest |
| | GET|HEAD | password/reset/{token} | password.reset | App\Http\Controllers\Auth\ResetPasswordController#showResetForm | web,guest |
| | GET|HEAD | recipes | recipes.index | App\Http\Controllers\RecipesController#index | web,auth |
| | POST | recipes | recipes.store | App\Http\Controllers\RecipesController#store | web,auth |
| | GET|HEAD | recipes/create | recipes.create | App\Http\Controllers\RecipesController#create | web,auth |
| | GET|HEAD | recipes/{id}/ingredients | ingredients.create | App\Http\Controllers\IngredientsController#create | web,auth |
| | POST | recipes/{id}/ingredients | ingredients.store | App\Http\Controllers\IngredientsController#store | web,auth |
| | GET|HEAD | recipes/{id}/steps | steps.create | App\Http\Controllers\StepsController#create | web,auth |
| | POST | recipes/{id}/steps | steps.store | App\Http\Controllers\StepsController#store | web,auth |
| | PUT|PATCH | recipes/{recipe} | recipes.update | App\Http\Controllers\RecipesController#update | web,auth |
| | DELETE | recipes/{recipe} | recipes.destroy | App\Http\Controllers\RecipesController#destroy | web,auth |
| | GET|HEAD | recipes/{recipe} | recipes.show | App\Http\Controllers\RecipesController#show | web,auth |
| | GET|HEAD | recipes/{recipe}/edit | recipes.edit | App\Http\Controllers\RecipesController#edit | web,auth |
| | POST | register | | App\Http\Controllers\Auth\RegisterController#register | web,guest |
| | GET|HEAD | register | register | App\Http\Controllers\Auth\RegisterController#showRegistrationForm | web,guest |
| | GET|HEAD | tags | tags.index | App\Http\Controllers\TagsController#index | web,auth |
| | POST | tags | tags.store | App\Http\Controllers\TagsController#store | web,auth |
| | GET|HEAD | tags/create | tags.create | App\Http\Controllers\TagsController#create | web,auth |
| | GET|HEAD | tags/{tag} | tags.show | App\Http\Controllers\TagsController#show | web,auth |
| | PUT|PATCH | tags/{tag} | tags.update | App\Http\Controllers\TagsController#update | web,auth |
| | DELETE | tags/{tag} | tags.destroy | App\Http\Controllers\TagsController#destroy | web,auth |
| | GET|HEAD | tags/{tag}/edit | tags.edit | App\Http\Controllers\TagsController#edit | web,auth |
+--------+-----------+--------------------------+--------------------+------------------------------------------------------------------------+--------------+