Settings API not saving

Question

I've been through this code a hundred times and I just can't spot what's wrong with it.

What it does:

✓ display options page, settings section, setting fields

✓ go through the sanitation function at the end

The very last function is just supposed to check that I have inserted the values correctly, but it keeps outputting:

Array ( [jazyk] => )

This is my first time using the Settings API. Thanks for helping.

add_action( 'admin_menu', 'experimental_plugin_page' );

// tick
function experimental_plugin_page() {
 
    add_options_page(
        'Experimental', // page <title>Title</title>
        'Experimental', // menu link text
        'manage_options', // capability to access the page
        'experimental', // page URL slug
        'experimental_page_content', // callback function /w content
        5 // priority
    );
 
}

function experimental_page_content () {
    ?>
    <div class="wrap">
        <h2>My plugin</h2>
        <form action="options.php" method="post">
        <?php
        // this is what the setting is called and how you retrieve the option later! (with get_options)
        settings_fields( 'experimental_plugin_options' );
        // slug name of the page whose settings sections you want to output
        // Use this in a settings page callback function to output all the 
        // sections and fields that were added to that $page with add_settings_section() and add_settings_field()
        do_settings_sections( 'experimental' );
        submit_button( 'Save Changes', 'primary' );
        ?>
        </form>
    </div>

<?php
}

// add an action on admin init
//
//
//
add_action ('admin_init', 'experimental_plugin_admin_init');

function experimental_plugin_admin_init () {
    // a/ register settings
    $args = array(
        'type' => 'string',
        // ↓ callable
        'sanitize_callback' => 'experimental_plugin_validate_options',
        'default' => NULL
        );
    register_setting ('experimental_plugin_options', 'experimental_plugin_options', $args);

    // b/ add a settings section
    add_settings_section (
        'experimental-section-main',
        'Experimentální plugin',
        // callable ↓ - echoes anything in the section
        'experimental_plugin_section_text',
        // page name
        'experimental'
    );

    // c/ add a settings field
    add_settings_field (
        'experimental-radio-field',
        'Jazyk aktualizovaného pole',
        // ↓ callback
        'experimental_plugin_setting_jazyk',
        'experimental',
        'experimental-section-main'
    );
};
function experimental_plugin_section_text() {
    echo '<p>Nastavte jazyk.</p>';
    };

function experimental_plugin_setting_jazyk () {
    // Get option 'beast_mode' value from the database
    // Set to 'disabled' as a default if the option does not exist
    $options = get_option( 'experimental_plugin_options', [ 'jazyk' => 'EN' ] );
    $jazyk = $options['jazyk'];
    // Define the radio button options
    $items = array( 'EN', 'CZ' );
    /*$jazyk = get_option ('experimental_plugin_options');*/
    foreach( $items as $item ) {
    // Loop the two radio button options and select if set in the option value
    echo "<label><input " . checked( $jazyk, $item, false ) . "
    value='" . esc_attr( $item ) . "' name='experimental_plugin_options
    [jazyk]'
    type='radio'/> " . esc_html( $item ) . "</label><br/>";
    }
    }

    function experimental_plugin_validate_options ($input) {
        $input['jazyk'] = sanitize_text_field( $input['jazyk'] );
        return $input;
    };

    add_action('admin_init', 'justshow');
    function justshow () {
        $output = get_option('experimental_plugin_options');
        print_r($output);
    }

Answer 1

It's working. I just got rid of the $jazyk variable and made the value I was saving a simple string, not an array, which was actually all I needed.