Hook um_email_send_subject

um_email_send_subject.php

<?php

/**
 * Hook: um_email_send_subject
 *
 * Type: filter
 *
 * Description: Change email notification subject.
 * Used in the core to translate email subject.
 *
 * @example https://github.com/ultimatemember/ultimatemember/blob/master/includes/core/class-mail.php#L439
 * @link    https://docs.ultimatemember.com/article/1113-umemailsendsubject
 *
 * @package um\core
 * @see     um\core\Mail::send()
 * @since   2.0
 * @version 3.0
 *
 * @param string $subject  Email subject.
 * @param string $template Template key.
 *
 * @return string Email subject.
 */
function my_email_send_subject( $subject, $template ) {
	// your code here.
	return $subject;
}
add_filter( 'um_email_send_subject', 'my_email_send_subject', 10, 2 );