This snippet enables a custom template to be used for when a member completes checkout for an addon. Look for "Checkout - Paid - Addon" in the template list. REQUIRES: PMPro, PMPro Addon Packages, and PMPro Email Templates Add On

pmpro-addon-checkout-email-template.php

<?php

/**
 * Register the custom checkout template for addon package purchases.
 *
 * @param array $templates The list of templates.
 *
 * @return array The list of templates.
 */
function my_addon_checkout_template_register_template( $templates ) {
	$templates['checkout_addon'] = array(
		'subject'     => __( 'Your addon confirmation for !!sitename!!', 'pmproet' ),
		'description' => __( 'Checkout - Paid - Addon', 'pmproet'),
	);

	return $templates;
}

add_filter( 'pmproet_templates', 'my_addon_checkout_template_register_template' );

/**
 * Set the custom checkout template for addon package purchases.
 *
 * @param string $template The template to use for the email.
 *
 * @return string The template to use for the email.
 */
function my_addon_checkout_template_set_template( $template ) {
	$templates_to_override = [
		'checkout_paid',
		'checkout_check',
		'checkout_express',
		'checkout_free',
	];

	// We should only override the template we want to.
	if ( ! in_array( $template, $templates_to_override, true ) ) {
		return $template;
	}

	// Check if the addon ID is set.
	if ( empty( $_REQUEST['ap'] ) ) {
		return $template;
	}

	return 'checkout_addon';
}

add_filter( 'pmpro_email_template', 'my_addon_checkout_template_set_template' );