Send a custom email when a user checks out for a pmpro level.

send_custom_email.php

<?php

/**
 * Add this code to your PMPro Customizations Plugin - http://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 * This function below sends a custom HTML email to the user that checks out for a pmpro membership level, easily extendible to send to admins, or specific users and so on.
 * Website: https://paidmembershipspro.com
 */

//let's send a custom email after user checkouts. This will not send an email if an admin changes user's level inside member area.
function custom_email_after_checkout( $user_id, $morder ){

		$user_details = get_userdata( $user_id ); //get user data for user checking out.

		$my_email = new PMProEmail();

		$my_email->email = $user_details->user_email; //who to send the email to - send to user that is checking out.
		$my_email->subject = 'This is a custom subject header'; //change this to the header you would like to use.
		$my_email->template = 'My Custom Email'; //custom name of email template.

		$my_email->body = '<p>Hi there,</p>'; //header of body content goes here
		$my_email->body .= '<p>Thank you for your purchase. {Change this text} </p>'; //body content goes here.
		$my_email->body .= '<p>Best Regards,</p> My Site Name.'; //footer content goes here.

		$my_email->sendEmail();

}

add_action( 'pmpro_after_checkout', 'custom_email_after_checkout', 10, 2 );

This gives me a "Fatal error: Uncaught ArgumentCountError:" , until I remove $morder.

Also, can email variables like !!billing_address!! be used in the body. If yes, how can they be added?

Updated the gist @kimwhite, passed in the '2' on last line to force the amount of parameters passed through.