Ttdfjt

I'm developing Magento 2 extension. I've added controller_action_predispatch_checkout event observer and trying to add a error message via ManagerInterface.

events.xml:

<event name="controller_action_predispatch_checkout">
 <observer name="controller_action_predispatch_checkout" instance="<namespace><module>ObserverCheckoutPredispatchObserver" />
</event>

CheckoutPredispatchObserver.php:

class CheckoutPredispatchObserver implements MagentoFrameworkEventObserverInterface 

private $messageManager;

public function __construct(MagentoFrameworkMessageManagerInterface $messageManager) 
 $this->messageManager = $messageManager; 


public function execute(MagentoFrameworkEventObserver $observer) 
 $this->messageManager->addErrorMessage("Custom error message");

However, my error message is not displayed in checkout page:

Instead, I can see my error message twice in checkout success page:

How can I make my error message appear in Checkout page but not in
further pages?

Try this event

checkout_onepage_controller_success_action

$this->_eventManager->dispatch(
 'checkout_onepage_controller_success_action',
 ['order_ids' => [$session->getLastOrderId()]]
);

These are all checkout events

1) checkout_directpost_placeOrder

$this->eventManager->dispatch(
 'checkout_directpost_placeOrder',
 [
 'result' => $result,
 'action' => $this
 ]);

2) checkout_cart_add_product_complete

$this->_eventManager->dispatch(
 'checkout_cart_add_product_complete',
 ['product' => $product, 'request' => $this->getRequest(), 'response' => $this->getResponse()]);

3) checkout_cart_update_item_complete

$this->_eventManager->dispatch(
 'checkout_cart_update_item_complete',
 ['item' => $item, 'request' => $this->getRequest(), 'response' => $this->getResponse()]);

4) checkout_controller_onepage_saveOrder

$this->_eventManager->dispatch(
 'checkout_controller_onepage_saveOrder',
 [
'result' => $result,
'action' => $this
 ]);

5) checkout_onepage_controller_success_action

$this->_eventManager->dispatch(
 'checkout_onepage_controller_success_action',
 ['order_ids' => [$session->getLastOrderId()]]);

6) checkout_allow_guest

$this->_eventManager->dispatch(
 'checkout_allow_guest',
 ['quote' => $quote, 'store' => $store, 'result' => $result]);

7) checkout_cart_product_add_after

$this->_eventManager->dispatch(
 'checkout_cart_product_add_after',
 ['quote_item' => $result, 'product' => $product]);

8) checkout_cart_update_items_before

$this->_eventManager->dispatch(
 'checkout_cart_update_items_before',
 ['cart' => $this, 'info' => $infoDataObject]);

9) checkout_cart_update_items_after

$this->_eventManager->dispatch(
 'checkout_cart_update_items_after',
 ['cart' => $this, 'info' => $infoDataObject]);

10) checkout_cart_save_before

$this->_eventManager->dispatch('checkout_cart_save_before', ['cart' => $this]);

11) checkout_cart_save_after

$this->_eventManager->dispatch('checkout_cart_save_after', ['cart' => $this]);

12) checkout_cart_product_update_after

$this->_eventManager->dispatch(
'checkout_cart_product_update_after',
['quote_item' => $result, 'product' => $product]);

13) custom_quote_process

$this->_eventManager->dispatch('custom_quote_process', ['checkout_session' => $this]);

14) checkout_quote_init

$this->_eventManager->dispatch('checkout_quote_init', ['quote' => $quote]);

15) load_customer_quote_before

$this->_eventManager->dispatch('load_customer_quote_before', ['checkout_session' => $this]);

16) checkout_quote_destroy

$this->_eventManager->dispatch('checkout_quote_destroy', ['quote' => $this->getQuote()]);

17) restore_quote

$this->_eventManager->dispatch('restore_quote', ['order' => $order, 'quote' => $quote]);

18) checkout_type_onepage_save_order_after

$this->_eventManager->dispatch(
'checkout_type_onepage_save_order_after',
['order' => $order, 'quote' => $this->getQuote()]);

19) checkout_submit_all_after

$this->_eventManager->dispatch(
 'checkout_submit_all_after',
 [
'order' => $order,
'quote' => $this->getQuote()
 ]);

20) checkout_multishipping_refund_all

$this->_eventManager->dispatch('checkout_multishipping_refund_all', ['orders' => $orders]);