Catch Form value at AJAX Form submit

I am working on a Custom Plugin. I have below JavaScript code.

const sent_urls = () => {
        const formData = new FormData();
        formData.append('action', 'start_parsing');
        formData.append('of_start_parsing_nonce', of_start_parsing_nonce.value);
        formData.append('urls', urls.slice(offset, offset + limit));

        formData.append( 'category_fans', category_fans );  //This is added by me

        fetch(ajaxurl, {
            method: 'POST',
            body: formData
        }).then(response => {
            if (!response.ok) {
                throw new Error('Network response was not ok');
            }
            return response.json();
        }).then(data => {
            if (data.error) {
                throw new Error(data.error);
            }

            if (!data.result) {
                throw new Error('Unknown error');
            }

            added += data.result.added;
            exists += data.result.exists;
            error_urls = error_urls.concat(data.result.error);
            offset += limit;
            count_urls.textContent = 'Imported ' + all_urls + ' urls. ' + 'Added ' + added + ' urls. Exists ' + exists + ' urls. ' + 'Error ' + error_urls.length + ' urls.';

            if (offset >= urls.length) {
                enable();

                alert.show_success('Parsing complete. Added ' + added + ' urls. Exists ' + exists + ' urls.');

                if (error_urls.length > 0) {
                    textarea.value = error_urls.join('\n');
                } else {
                    textarea.value = '';
                }

                offset = 0;
                added = 0;
                exists = 0;
                error_urls = [];

                return;
            } else {
                sent_urls();
            }
        }).catch(error => {
            enable();
            alert.show_warn(error);
        });
    }

My AdminAjax class is like below.

<?php


namespace OnlyFansPlugin;

use PhpOffice\PhpSpreadsheet\IOFactory;

use function get_class_methods;


class AdminAjax {
    /**
     * The function is a constructor that registers actions.
     */
    public function __construct() {
        $this->register_actions();
    }

    /**
     * The function "start_parsing" starts parsing.
     */
    public function start_parsing() {

        if ( ! $this->verify( 'start_parsing' ) ) {
            echo wp_json_encode(
                array(
                    'error' => 'Error request.',
                )
            );
            wp_die();
        }



        $category = $this->get_post_field( 'category_fans', '' );

        error_log(print_r($category));



        $urls_str = $this->get_post_field( 'urls', '' );

        $urls = explode( ',', $urls_str );




        if ( ! $urls ) {
            echo wp_json_encode(
                array(
                    'error' => 'Error: wrong list urls.',
                )
            );
            wp_die();
        }

        $added  = 0;
        $error  = array();
        $exists = 0;

        foreach ( $urls as $raw_url ) {
            $url = trim( $raw_url );

            if ( '' === $url || ! filter_var( $url, FILTER_VALIDATE_URL ) ) {
                continue;
            }

            $parser  = new Parser( $url );
            $account = $parser->get_account();

            if (!$account->is_valid()) {
                $error[] = 'Error on parse: ' . $url;
                continue;
            }

            // if account not exists.
            if ( $account->get_post_id() === 0 ) {
                $success = $account->save();

                if ( $success ) {
                    $added += 1;
                } else {
                    $error[] = 'Error on save: ' . $url;
                }
            } else {
                // if account exists then delete images.
                $account->delete_images();
                $exists += 1;
            }
        }

        $response = array(
            'result' => array(
                'added'  => $added,
                'error'  => $error,
                'exists' => $exists,
            ),
        );

        echo wp_json_encode( $response );
        wp_die();
    }

    /**
     * The function "get_nonce_field" generates a nonce field for a form.
     *
     * @param string $action_name The "action_name" parameter is a string that represents the name of the action
     * or form being verified. It is used to generate the nonce and action names for the form.
     *
     * @return void
     */
    public static function get_nonce_field( string $action_name ) {
        wp_nonce_field( "of_{$action_name}_action", "of_{$action_name}_nonce" );
    }

    /**
     * The function "register_actions" registers actions.
     *
     * @return void
     */
    private function register_actions() {
        $methods = get_class_methods( $this );

        foreach ( $methods as $method ) {
            if ( '_' === substr( $method, 0, 1 ) ) {
                continue;
            }

            if ( 'register_actions' === $method ) {
                continue;
            }

            add_action( 'wp_ajax_' . $method, array( $this, $method ) );
            add_action( 'wp_ajax_nopriv_' . $method, array( $this, $method ) );
        }
    }

    /**
     * The function "verify" verifies the nonce for a form.
     *
     * @param string $action_name The "action_name" parameter is a string that represents the name of the action
     * or form being verified. It is used to generate the nonce and action names for the form.
     *
     * @return bool true if the nonce is verified, false if it is not verified.
     */
    private function verify( string $action_name ): bool {
        $nonce  = "of_{$action_name}_nonce";
        $action = "of_{$action_name}_action";

        return isset( $_POST[ $nonce ] ) && wp_verify_nonce( $_POST[ $nonce ], $action );
    }

    /**
     * The function "get_post_field" returns the value of the $_POST field.
     *
     * @param string $key The "key" parameter is a string that represents the name of the $_POST field.
     * @param mixed $default The "default" parameter is the default value if the $_POST field is not set.
     *
     * @return mixed
     */
    private function get_post_field( string $key, $default = '' ) {
        return isset( $_POST[ $key ] ) ? wp_unslash( $_POST[ $key ] ) : $default;
    }
}

I would like to catch Category like this error_log(print_r($category));