GiveWP Transaction ID Email Tag

add_give_transaction_id_tag.php

<?php
function add_give_transaction_id_tag() {
	give_add_email_tag(
		array(
			'tag'      => 'transaction_id', // The tag name.
			'desc'     => __( 'Outputs the payment gateway transaction ID', 'give' ),
			'func'     => 'custom_transaction_id_tag', // Callback to function below.
			'context'  => 'donation', // This tag can be for both admin and donor notifications.
			'is_admin' => false, // default is false. This is here to simply display it as an option.
        )
    );
}

add_action( 'give_add_email_tags', 'add_give_transaction_id_tag' );

function custom_transaction_id_tag( $tag_args ) {

	$payment_id = $tag_args['payment_id'];
	
	$transaction_id = give_get_payment_transaction_id( $payment_id );

	if ( ! empty( $transaction_id) ) {
		return $transaction_id;
	} 
	return;
}