balance-on-submission.php

<?php

/**
 * Plugin Name: Forminator
 * Description: Decrease user balance on form submission.
 * Author: Patrick Freitas @ WPMUDEV
 * Author URI: https://premium.wpmudev.org
 * License: GPLv2 or later
 */

add_filter(
    'forminator_custom_form_submit_errors',
    function ($submit_errors, $form_id, $field_data_array) {

        // Add your form IDs here.
        $form_ids = array(8);

        // Change this to the message that you want to show.
        $message = "You don't have enough balance.";
        //$meta_key = 'account_balance'; // edit here if it is a different field name

        // chnage meta key based on form id
        $meta_key_mapping = [
            8 => 'account_balance_form_8',
            10 => 'account_balance_form_10',
        ];

        if (in_array(intval($form_id), $form_ids, true)) {

            $current_user_id = get_current_user_id();

            if ($current_user_id) {

                // get meta value from logged in user
                //$user_balance = get_user_meta($current_user_id, $meta_key, true);
                $user_balance = get_user_meta($current_user_id, $meta_key_mapping[$form_id], true);

                // not enough balance
                if (intval($user_balance) < 1) {

                    add_filter('forminator_custom_form_invalid_form_message', function ($invalid_form_message, $module_id) use ($message) {
                        return $message;
                    }, 9999, 2);

                    $submit_errors[]['submit'] = $message;

                }else{

                    // decrease balance
                    //update_user_meta($current_user_id, $meta_key, intval($user_balance) - 1);
                    update_user_meta($current_user_id, $meta_key_mapping[$form_id], intval($user_balance) - 1);
                }
                
            }
        }

        return $submit_errors;
    },
    15,
    3
);