leaky-paywall-stop-specific-welcome-emails.php

<?php

add_filter('leaky_paywall_send_new_email', 'zeen_filter_send_emails', 10, 2 );

function zeen_filter_send_emails( $send, $user_id ) {

    $mode     = leaky_paywall_get_current_mode();
    $site     = leaky_paywall_get_current_site();
    $level_id   = get_user_meta($user_id, '_issuem_leaky_paywall_' . $mode . '_level_id' . $site, true);

    // enter the level ids where you want to stop the welcome email from sending
    $do_not_send = array(3, 4);

    if ( in_array( $level_id, $do_not_send ) ) {
        return false;
    }

    return $send;

}