Have users update their billing information in Stripe Customer Portal.

stripe_customer_portal.php

<?php

// Copy from below here...

/**
 * Have users update their billing information in Stripe Customer Portal.
 *
 * NOTE: Before using Stripe Customer Portal, you must first enable it by saving the
 * customer portal settings page here:
 * https://dashboard.stripe.com/settings/billing/portal (For live mode)
 * https://dashboard.stripe.com/test/settings/billing/portal (For test mode)
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
add_action( 'pmpro_billing_preheader', 'my_pmpro_billing_preheader_redirect_to_stripe' );
function my_pmpro_get_customer_portal_url( $customer_id ) {
	try {
		$session = \Stripe\BillingPortal\Session::create([
			'customer' => $customer_id,
			'return_url' => get_site_url(),
		]);
		return $session->url;
	} catch ( Exception $e ) {
		return '';
	}
}

function my_pmpro_billing_preheader_redirect_to_stripe() {
	global $besecure, $gateway, $show_paypal_link, $show_check_payment_instructions;
	$user_order = new MemberOrder();
	$user_order->getLastMemberOrder( null, array( 'success', 'pending' ) );


	$stripe = new PMProGateway_stripe();
	$customer = $stripe->get_customer_for_user( $user_order->user_id );
	if ( empty( $customer->id ) ) {
		return;
	}

	$customer_portal_url = my_pmpro_get_customer_portal_url( $customer->id );
	if ( ! empty( $customer_portal_url ) ) {
		wp_redirect( $customer_portal_url );
		exit;
	}
}