Use below CSS for hiding discount block.
.checkout-index-index .payment-option._collapsible.opc-payment-additional.discount-code { display: none; }
Edit
app/code/vendor/Module/view/frontend/layout/checkout_index_index.xml
or
app/design/frontend/Vendor/theme/Magento_Checkout/layout/checkout_index_index.xml
you can also remove discount block using 'checkout_index_index.xml'
@Prashant is also correct;
<?xml version="1.0"?> <page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="checkout" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd"> <body> <referenceBlock name="checkout.root"> <arguments> <argument name="jsLayout" xsi:type="array"> <item name="components" xsi:type="array"> <item name="checkout" xsi:type="array"> <item name="children" xsi:type="array"> <item name="steps" xsi:type="array"> <item name="children" xsi:type="array"> <item name="billing-step" xsi:type="array"> <item name="children" xsi:type="array"> <item name="payment" xsi:type="array"> <item name="children" xsi:type="array"> <item name="afterMethods" xsi:type="array"> <item name="children" xsi:type="array"> <item name="discount" xsi:type="array"> <item name="config" xsi:type="array"> <item name="componentDisabled" xsi:type="boolean">true</item> </item> </item> </item> </item> </item> </item> </item> </item> </item> </item> </item> </item> </item> </argument> </arguments> </referenceBlock> </body> </page>