AutomateWoo - Action function to change subscription next payment date

file.php

<?php
/**
 * AutomateWoo action function to extend a subscription by 3 months.
 *
 * A note will be added to the subscription.
 *
 * Ensures that the dates near the end of the month are logically handled and do not shift to the start of the following month.
 * 
 * Custom action function docs: https://automatewoo.com/docs/actions/custom-functions/
 *
 * @param $workflow AutomateWoo\Workflow
 */
function my_extend_subscription_automatewoo_action( $workflow ) {
	// Valid options are: day, week, month or year
	$date_period = 'month';
	// E.g. extend by 3 months.
	$number_of_periods = 3;

	$subscription = $workflow->data_layer()->get_subscription();
	$payment_date = $subscription->get_date( 'next_payment' );

	if ( ! $payment_date ) {
		return;
	}

	$payment_date_timestamp = wcs_date_to_time( $payment_date );
	$new_payment_date_timestamp = wcs_add_time( $number_of_periods, $date_period, $payment_date_timestamp );

	// Update the next payment date
	$subscription->update_dates(
		array(
			'next_payment' => gmdate( 'Y-m-d H:i:s', $new_payment_date_timestamp ),
		)
	);

	// Add note to subscription
	$subscription->add_order_note(
		sprintf(
			'Subscription next payment date was extended from %s to %s by workflow: %s',
			gmdate( wc_date_format(), $payment_date_timestamp ),
			gmdate( wc_date_format(), $new_payment_date_timestamp ),
			$workflow->get_title()
		)
	);
}

Dan-
EDIT: code works on php. 7.1, does not work on 7.4 :(
I'd like to extend a quarterly subscription by 1 month (so when the customer purchases a quarterly subscription, their 1st recurring payment date will be 4 months out, instead of 3). However, I'd like to limit this to only new subscribers. In the Automate Woo workflow, I've added "parent" under subscription order types. Unfortunately it did not work when I tested it. Currently I have php 7.4. It worked on 7.1.
The product is a variable subscription product - I've only selected the quarterly variable for this. Is there anything I can do to limit it like that? Thank you.

Hi Dan, I don't get how you can moodify your snippet to move the 'next_payment' day to the first day of each month...
Thank's