AhmedNadar PRO said about 3 years ago on StimulusJS, Active Storage and DropzoneJS :
Here is the response from Network tab inside Firefox Dev Tools.

ActionController::InvalidAuthenticityToken at /rails/active_storage/direct_uploads
==================================================================================

ActionController::InvalidAuthenticityToken

> To access an interactive console with this error, point your browser to: /__better_errors


actionpack (6.1.3) lib/action_controller/metal/request_forgery_protection.rb, line 211
--------------------------------------------------------------------------------------

``` ruby
  206           def initialize(controller)
  207             @controller = controller
  208           end
  209   
  210           def handle_unverified_request
> 211             raise ActionController::InvalidAuthenticityToken
  212           end
  213         end
  214       end
  215   
  216       private
```

App backtrace
-------------



Full backtrace
--------------

 - actionpack (6.1.3) lib/action_controller/metal/request_forgery_protection.rb:211:in `handle_unverified_request'
 - actionpack (6.1.3) lib/action_controller/metal/request_forgery_protection.rb:243:in `handle_unverified_request'
 - devise (4.7.3) lib/devise/controllers/helpers.rb:255:in `handle_unverified_request'
 - actionpack (6.1.3) lib/action_controller/metal/request_forgery_protection.rb:238:in `verify_authenticity_token'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:427:in `block in make_lambda'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:198:in `block (2 levels) in halting'
 - actionpack (6.1.3) lib/abstract_controller/callbacks.rb:34:in `block (2 levels) in <module:Callbacks>'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:199:in `block in halting'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:512:in `block in invoke_before'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:512:in `invoke_before'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:115:in `block in run_callbacks'
 - actiontext (6.1.3) lib/action_text/rendering.rb:20:in `with_renderer'
 - actiontext (6.1.3) lib/action_text/engine.rb:55:in `block (4 levels) in <class:Engine>'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:126:in `block in run_callbacks'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:137:in `run_callbacks'
 - actionpack (6.1.3) lib/abstract_controller/callbacks.rb:41:in `process_action'
 - actionpack (6.1.3) lib/action_controller/metal/rescue.rb:22:in `process_action'
 - actionpack (6.1.3) lib/action_controller/metal/instrumentation.rb:34:in `block in process_action'
 - activesupport (6.1.3) lib/active_support/notifications.rb:203:in `block in instrument'
 - activesupport (6.1.3) lib/active_support/notifications/instrumenter.rb:24:in `instrument'
 - activesupport (6.1.3) lib/active_support/notifications.rb:203:in `instrument'
 - actionpack (6.1.3) lib/action_controller/metal/instrumentation.rb:33:in `process_action'
 - actionpack (6.1.3) lib/action_controller/metal/params_wrapper.rb:249:in `process_action'
 - activerecord (6.1.3) lib/active_record/railties/controller_runtime.rb:27:in `process_action'
 - actionpack (6.1.3) lib/abstract_controller/base.rb:165:in `process'
 - actionview (6.1.3) lib/action_view/rendering.rb:39:in `process'
 - actionpack (6.1.3) lib/action_controller/metal.rb:190:in `dispatch'
 - actionpack (6.1.3) lib/action_controller/metal.rb:254:in `dispatch'
 - actionpack (6.1.3) lib/action_dispatch/routing/route_set.rb:50:in `dispatch'
 - actionpack (6.1.3) lib/action_dispatch/routing/route_set.rb:33:in `serve'
 - actionpack (6.1.3) lib/action_dispatch/journey/router.rb:50:in `block in serve'
 - actionpack (6.1.3) lib/action_dispatch/journey/router.rb:32:in `serve'
 - actionpack (6.1.3) lib/action_dispatch/routing/route_set.rb:842:in `call'
 - warden (1.2.9) lib/warden/manager.rb:36:in `block in call'
 - warden (1.2.9) lib/warden/manager.rb:34:in `call'
 - rack (2.2.3) lib/rack/tempfile_reaper.rb:15:in `call'
 - rack (2.2.3) lib/rack/etag.rb:27:in `call'
 - rack (2.2.3) lib/rack/conditional_get.rb:40:in `call'
 - rack (2.2.3) lib/rack/head.rb:12:in `call'
 - actionpack (6.1.3) lib/action_dispatch/http/permissions_policy.rb:22:in `call'
 - actionpack (6.1.3) lib/action_dispatch/http/content_security_policy.rb:18:in `call'
 - rack (2.2.3) lib/rack/session/abstract/id.rb:266:in `context'
 - rack (2.2.3) lib/rack/session/abstract/id.rb:260:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/cookies.rb:689:in `call'
 - activerecord (6.1.3) lib/active_record/migration.rb:601:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/callbacks.rb:27:in `block in call'
 - activesupport (6.1.3) lib/active_support/callbacks.rb:98:in `run_callbacks'
 - actionpack (6.1.3) lib/action_dispatch/middleware/callbacks.rb:26:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/executor.rb:14:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/actionable_exceptions.rb:18:in `call'
 - better_errors (2.9.1) lib/better_errors/middleware.rb:87:in `protected_app_call'
 - better_errors (2.9.1) lib/better_errors/middleware.rb:82:in `better_errors_call'
 - better_errors (2.9.1) lib/better_errors/middleware.rb:60:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/debug_exceptions.rb:29:in `call'
 - web-console (4.1.0) lib/web_console/middleware.rb:132:in `call_app'
 - web-console (4.1.0) lib/web_console/middleware.rb:28:in `block in call'
 - web-console (4.1.0) lib/web_console/middleware.rb:17:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
 - railties (6.1.3) lib/rails/rack/logger.rb:37:in `call_app'
 - railties (6.1.3) lib/rails/rack/logger.rb:26:in `block in call'
 - activesupport (6.1.3) lib/active_support/tagged_logging.rb:99:in `block in tagged'
 - activesupport (6.1.3) lib/active_support/tagged_logging.rb:37:in `tagged'
 - activesupport (6.1.3) lib/active_support/tagged_logging.rb:99:in `tagged'
 - railties (6.1.3) lib/rails/rack/logger.rb:26:in `call'
 - sprockets-rails (3.2.2) lib/sprockets/rails/quiet_assets.rb:13:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/request_id.rb:26:in `call'
 - rack (2.2.3) lib/rack/method_override.rb:24:in `call'
 - rack (2.2.3) lib/rack/runtime.rb:22:in `call'
 - activesupport (6.1.3) lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/executor.rb:14:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/static.rb:24:in `call'
 - rack (2.2.3) lib/rack/sendfile.rb:110:in `call'
 - actionpack (6.1.3) lib/action_dispatch/middleware/host_authorization.rb:98:in `call'
 - webpacker (5.2.1) lib/webpacker/dev_server_proxy.rb:25:in `perform_request'
 - rack-proxy (0.6.5) lib/rack/proxy.rb:57:in `call'
 - railties (6.1.3) lib/rails/engine.rb:539:in `call'
 - puma (5.2.2) lib/puma/configuration.rb:248:in `call'
 - puma (5.2.2) lib/puma/request.rb:76:in `block in handle_request'
 - puma (5.2.2) lib/puma/thread_pool.rb:337:in `with_force_shutdown'
 - puma (5.2.2) lib/puma/request.rb:75:in `handle_request'
 - puma (5.2.2) lib/puma/server.rb:431:in `process_client'
 - puma (5.2.2) lib/puma/thread_pool.rb:145:in `block in spawn_thread'