WooCommerce - rename the "Have a Coupon?" message and "Apply Coupon" field on the checkout

wc-rename-checkout-coupon-field.php

<?php

// rename the "Have a Coupon?" message on the checkout page
function woocommerce_rename_coupon_message_on_checkout() {

	return 'Have a Promo Code?' . ' <a href="#" class="showcoupon">' . __( 'Click here to enter your code', 'woocommerce' ) . '</a>';
}
add_filter( 'woocommerce_checkout_coupon_message', 'woocommerce_rename_coupon_message_on_checkout' );

// rename the coupon field on the checkout page
function woocommerce_rename_coupon_field_on_checkout( $translated_text, $text, $text_domain ) {

	// bail if not modifying frontend woocommerce text
	if ( is_admin() || 'woocommerce' !== $text_domain ) {
		return $translated_text;
	}

	if ( 'Coupon code' === $text ) {
		$translated_text = 'Promo Code';
	
	} elseif ( 'Apply Coupon' === $text ) {
		$translated_text = 'Apply Promo Code';
	}

	return $translated_text;
}
add_filter( 'gettext', 'woocommerce_rename_coupon_field_on_checkout', 10, 3 );

This is not working for me as well.

@Ruben2600 try to change with css.

.cart .coupon .button {
    background-color: #000000;
}

replace it with proper css class (applied in your theme).

I just went through this and this code snippet is working for me:

/**
 * Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function bt_rename_coupon_field_on_cart( $translated_text, $text, $text_domain ) {
	// bail if not modifying frontend woocommerce text
	if ( is_admin() || 'woocommerce' !== $text_domain ) {
		return $translated_text;
	}
	if ( 'Coupon:' === $text ) {
		$translated_text = 'Voucher Code:';
	}

	if ('Coupon has been removed.' === $text){
		$translated_text = 'Voucher code has been removed.';
	}

	if ( 'Apply coupon' === $text ) {
		$translated_text = 'Apply voucher';
	}

	if ( 'Coupon code' === $text ) {
		$translated_text = 'Voucher code';
	
	} 

	return $translated_text;
}
add_filter( 'gettext', 'bt_rename_coupon_field_on_cart', 10, 3 );

/**
 * Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function bt_rename_coupon_message_on_checkout() {
	return 'Have a voucher code?' . ' <a href="#" class="showcoupon">' . __( 'Click here to enter your code', 'woocommerce' ) . '</a>.';
}
add_filter( 'woocommerce_checkout_coupon_message', 'bt_rename_coupon_message_on_checkout' );

/**
 * Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function bt_rename_coupon_label( $err, $err_code=null, $something=null ){
	$err = str_ireplace("Coupon","voucher",$err);
	return $err;
}
add_filter( 'woocommerce_coupon_error', 'bt_rename_coupon_label', 10, 3 );
add_filter( 'woocommerce_coupon_message', 'bt_rename_coupon_label', 10, 3 );
add_filter( 'woocommerce_cart_totals_coupon_label', 'bt_rename_coupon_label',10, 1 );

Just posting it for easy reference for future developers, as it compiles others feedback in this thread, plus fixes missing bits of html in one of the comments.

Actually I've tweaked it to the following code now, just to catch a couple more edge cases:

/**
 * Soka - Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function soka_rename_coupon_field_on_cart( $translated_text, $text, $text_domain ) {
	// bail if not modifying frontend woocommerce text
	if ( is_admin() || 'woocommerce' !== $text_domain ) {
		return $translated_text;
	}
	if ( 'Coupon:' === $text ) {
		$translated_text = 'Voucher Code:';
	}

	if ('Coupon has been removed.' === $text){
		$translated_text = 'Voucher code has been removed.';
	}

	if ( 'Apply coupon' === $text ) {
		$translated_text = 'Redeem voucher';
	}

	if ( 'Coupon code' === $text ) {
		$translated_text = 'Voucher code';
	} 

	if ( 'If you have a coupon code, please apply it below.' === $text ) {
		$translated_text = 'If you have a voucher code, please apply it below.';
	} 

	return $translated_text;
}
add_filter( 'gettext', 'soka_rename_coupon_field_on_cart', 10, 3 );

/**
 * Soka - Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function soka_rename_coupon_message_on_checkout() {
	return 'Have a voucher code?' . ' <a href="#" class="showcoupon">' . __( 'Click here to enter your code', 'woocommerce' ) . '</a>.';
}
add_filter( 'woocommerce_checkout_coupon_message', 'soka_rename_coupon_message_on_checkout' );

/**
 * Soka - Change 'coupon' text to 'voucher'
 * @source https://gist.github.com/maxrice/8551024
 */
function soka_rename_coupon_label( $err, $err_code=null, $something=null ){
	$err = str_replace("Coupon","Voucher",$err);
	$err = str_replace("coupon","voucher",$err);
	return $err;
}
add_filter( 'woocommerce_coupon_error', 'soka_rename_coupon_label', 10, 3 );
add_filter( 'woocommerce_coupon_message', 'soka_rename_coupon_label', 10, 3 );
add_filter( 'woocommerce_cart_totals_coupon_label', 'soka_rename_coupon_label',10, 1 );

Bit late to the party, but is there a way to just hide / remove: 'Have a coupon? [Click here to enter your code]' and 'Coupon:'? I already made it so it automatically opens whenever you enter the checkout page. Thanks! :D