lp-email-after-renewal-payment.php

<?php

add_action( 'leaky_paywall_stripe_invoice_payment_succeeded', 'mysite_send_stripe_renewal_thank_you', 10, 2 );

function mysite_send_stripe_renewal_thank_you( $user, $invoice ) {

    if ( empty( $invoice->billing_reason ) || 'subscription_cycle' !== $invoice->billing_reason ) {
        return;
    }

    // Idempotency: Stripe retries webhooks. Don't email twice for the same invoice.
    $idempotency_key = 'mysite_renewal_email_' . $invoice->id;
    if ( get_transient( $idempotency_key ) ) {
        return;
    }
    set_transient( $idempotency_key, 1, WEEK_IN_SECONDS );

    $first_name = $user->first_name ? $user->first_name : 'there';
    $amount     = isset( $invoice->amount_paid ) ? number_format( $invoice->amount_paid / 100, 2 ) : '';
    $currency   = isset( $invoice->currency ) ? strtoupper( $invoice->currency ) : '';

    $subject  = 'Thank you for renewing your subscription';
    $message  = "Hi {$first_name},\n\n";
    $message .= "Your subscription renewal went through. Thank you for continuing to support us.\n\n";
    if ( $amount && $currency ) {
        $message .= "Amount renewed: {$amount} {$currency}\n\n";
    }
    $message .= "If you have any questions, just reply to this email.\n\n";
    $message .= "— The Publisher\n";

    wp_mail( $user->user_email, $subject, $message );
}