Reflectionexception Class App Http Controllers API Usercontroller does not exist

Question

When I try to hit the api/Register route, I get:

Reflectionexception Class App Http Controllers API Usercontroller does not exist

My Usercontroller

<?php
namespace App\Http\Controllers\API;
use Illuminate\Http\Request; 
use App\Http\Controllers\Controller; 
use App\User; 
use Illuminate\Support\Facades\Auth; 
use Validator;

class UserController extends Controller 
{
public $successStatus = 200;
/** 
     * login api 
     * 
     * @return \Illuminate\Http\Response 
     */ 
    public function login(){ 
        if(Auth::attempt(['email' => request('email'), 'password' => request('password')])){ 
            $user = Auth::user(); 
            $success['token'] =  $user->createToken('MyApp')-> accessToken; 
            return response()->json(['success' => $success], $this-> successStatus); 
        } 
        else{ 
            return response()->json(['error'=>'Unauthorised'], 401); 
        } 
    }
/** 
     * Register api 
     * 
     * @return \Illuminate\Http\Response 
     */ 
    public function register(Request $request) 
    { 
        $validator = Validator::make($request->all(), [ 
            'name' => 'required', 
            'email' => 'required|email', 
            'password' => 'required', 
            'c_password' => 'required|same:password', 
        ]);
if ($validator->fails()) { 
            return response()->json(['error'=>$validator->errors()], 401);            
        }
$input = $request->all(); 
        $input['password'] = bcrypt($input['password']); 
        $user = User::create($input); 
        $success['token'] =  $user->createToken('MyApp')-> accessToken; 
        $success['name'] =  $user->name;
return response()->json(['success'=>$success], $this-> successStatus); 
    }
/** 
     * details api 
     * 
     * @return \Illuminate\Http\Response 
     */ 
    public function details() 
    { 
        $user = Auth::user(); 
        return response()->json(['success' => $user], $this-> successStatus); 
    } 
}

My controller is in:

Laravel-api/app/Http/Controllers/API/Usercontroller

My route

<?php

use Illuminate\Http\Request;

/*
|--------------------------------------------------------------------------
| API Routes
|--------------------------------------------------------------------------
|
| Here is where you can register API routes for your application. These
| routes are loaded by the RouteServiceProvider within a group which
| is assigned the "api" middleware group. Enjoy building your API!
|
*/

Route::post('login', 'API\UserController@login');
Route::post('register', 'API\UserController@register');

Route::group(['middleware' => 'auth:api'], function(){
    Route::post('details', 'API\UserController@details');
});

Why does that happen? I tried to follow a tutorial I saw on the site Medium, followed exactly, I saw that some people had the same problem related to namespace, but I believe mine is already correct. Could someone help me?