Fluent form not working

my fluet form stop working and is showing this:

Fatal error: Uncaught Error: Call to undefined function FluentForm\Framework\Support\mb_strtoupper() in /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Support/Str.php:1318 Stack trace: #0 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Support/Str.php(1720): FluentForm\Framework\Support\Str::upper() #1 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Support/Str.php(1580): FluentForm\Framework\Support\Str::ucfirst() #2 [internal function]: FluentForm\Framework\Support\Str::FluentForm\Framework\Support\{closure}() #3 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Support/Str.php(1579): array_map() #4 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Database/Orm/Concerns/HasAttributes.php(613): FluentForm\Framework\Support\Str::studly() #5 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Database/Orm/Concerns/HasAttributes.php(2024): FluentForm\Framework\Database\Orm\Model->hasGetMutator() #6 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Database/Orm/Concerns/HasAttributes.php(500): FluentForm\Framework\Database\Orm\Model->transformModelValue() #7 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Database/Orm/Concerns/HasAttributes.php(453): FluentForm\Framework\Database\Orm\Model->getAttributeValue() #8 /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Database/Orm/Model.php(1989): FluentForm\Framework\Database\Orm\Model->getAttribute() #9 /home/mrsclean/public_html/wp-content/plugins/fluentform/app/Helpers/Helper.php(750): FluentForm\Framework\Database\Orm\Model->__get() #10 /home/mrsclean/public_html/wp-content/plugins/fluentform/app/Modules/Widgets/FluentFormWidget.php(104): FluentForm\App\Helpers\Helper::getForms() #11 /home/mrsclean/public_html/wp-content/plugins/fluentform/app/Modules/Widgets/FluentFormWidget.php(69): FluentForm\App\Modules\Widgets\FluentFormWidget->register_general_controls() #12 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(2435): FluentForm\App\Modules\Widgets\FluentFormWidget->register_controls() #13 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/widget-base.php(1049): Elementor\Controls_Stack->init_controls() #14 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(570): Elementor\Widget_Base->init_controls() #15 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/widget-base.php(185): Elementor\Controls_Stack->get_stack() #16 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(315): Elementor\Widget_Base->get_stack() #17 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(2524): Elementor\Controls_Stack->get_controls() #18 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(1161): Elementor\Controls_Stack->sanitize_settings() #19 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/element-base.php(624): Elementor\Controls_Stack->get_data() #20 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/widget-base.php(748): Elementor\Element_Base->get_raw_data() #21 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/element-base.php(629): Elementor\Widget_Base->get_raw_data() #22 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/element-base.php(629): Elementor\Element_Base->get_raw_data() #23 /home/mrsclean/public_html/wp-content/plugins/elementor/core/base/document.php(1105): Elementor\Element_Base->get_raw_data() #24 /home/mrsclean/public_html/wp-content/plugins/elementor/core/base/document.php(738): Elementor\Core\Base\Document->get_elements_raw_data() #25 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/base/controls-stack.php(1071): Elementor\Core\Base\Document->get_initial_config() #26 /home/mrsclean/public_html/wp-content/plugins/elementor/core/editor/loader/common/editor-common-scripts-settings.php(40): Elementor\Controls_Stack->get_config() #27 /home/mrsclean/public_html/wp-content/plugins/elementor/core/editor/loader/v2/editor-v2-loader.php(172): Elementor\Core\Editor\Loader\Common\Editor_Common_Scripts_Settings::get() #28 /home/mrsclean/public_html/wp-content/plugins/elementor/core/editor/editor.php(355): Elementor\Core\Editor\Loader\V2\Editor_V2_Loader->enqueue_scripts() #29 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(341): Elementor\Core\Editor\Editor->enqueue_scripts() #30 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters() #31 /home/mrsclean/public_html/wp-includes/plugin.php(522): WP_Hook->do_action() #32 /home/mrsclean/public_html/wp-includes/script-loader.php(2311): do_action() #33 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(341): wp_enqueue_scripts() #34 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters() #35 /home/mrsclean/public_html/wp-includes/plugin.php(522): WP_Hook->do_action() #36 /home/mrsclean/public_html/wp-includes/general-template.php(3197): do_action() #37 /home/mrsclean/public_html/wp-content/plugins/elementor/includes/editor-templates/editor-wrapper.php(35): wp_head() #38 /home/mrsclean/public_html/wp-content/plugins/elementor/core/editor/loader/v2/editor-v2-loader.php(222): include(‘/home/mrsclean/…’) #39 /home/mrsclean/public_html/wp-content/plugins/elementor/core/editor/editor.php(160): Elementor\Core\Editor\Loader\V2\Editor_V2_Loader->print_root_template() #40 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(341): Elementor\Core\Editor\Editor->init() #41 /home/mrsclean/public_html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters() #42 /home/mrsclean/public_html/wp-includes/plugin.php(522): WP_Hook->do_action() #43 /home/mrsclean/public_html/wp-admin/admin.php(424): do_action() #44 /home/mrsclean/public_html/wp-admin/post.php(12): require_once(‘/home/mrsclean/…’) #45 {main} thrown in /home/mrsclean/public_html/wp-content/plugins/fluentform/vendor/wpfluent/framework/src/WPFluent/Support/Str.php on line 1318

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