fluent-form-get-param-values.php

/*
* Input Default Values form url array values
* {thrivecart.customer.email}
*/
add_filter('fluentform_editor_shortcode_callback_group_thrivecart', function ($handler, $form, $handlerArray) {
    $handler = \FluentForm\App\Services\FormBuilder\EditorShortcodeParser::parseValue($handler);
    $handlerKey = array_pop($handler);
    if (!$handlerKey) {
        return '';
    }
    $urlValue = FluentForm\Framework\Helpers\ArrayHelper::get($_GET, $handlerKey);
    
    //sanitize here as your need
    return $urlValue;
}, 10, 3);