Class App\Http\Controllers\api\ApiController located in ./app/Http/Controllers/API/Apicontroller.php does not comply with psr-4 autoloading standard. Skipping.
./app/Http/Controllers/API/Apicontroller.php
переименовать в ./app/Http/Controllers/API/ApiController.php
Script @php artisan package:discover --ansi handling the post-autoload-dump event returned with error code 255
Class App\Http\Controllers\api\ApiController located in ./app/Http/Controllers/API/Apicontroller.php
я вижу что у вас Api
папка в разных регистрах указана, название файла ApiController
тоже в разных регистрах. Сравните эти два рута и увидите где ошибки Script @php artisan package:discover --ansi handling the post-autoload-dump event returned with error code 255