Add Custom Meta Field to Custom Taxonomy

lx_add_meta_to_tax.php

<?php

// Using the custom taxonomy "series" as an example


    // Add term page
    function lx_add_meta_field_to_taxonomy() {
        ?>
        <div class="form-field">
            <label for="term_meta[custom_term_meta]"><?php _e( 'Example meta field', 'yourtheme' ); ?></label>
            <input type="text" name="term_meta[custom_term_meta]" id="term_meta[custom_term_meta]" value="">
            <p class="description"><?php _e( 'Enter a value for this field','yourtheme' ); ?></p>
        </div>
        <?php
    }
    add_action( 'series_add_form_fields', 'lx_add_meta_field_to_taxonomy', 10, 2 );

    // Edit term page
    function lx_taxonomy_edit_meta_field($term) {
     
        // put the term ID into a variable
        $t_id = $term->term_id;
     
        // retrieve the existing value(s) for this meta field. This returns an array
        $term_meta = get_option( "taxonomy_$t_id" ); ?>
        <tr class="form-field">
        <th scope="row" valign="top"><label for="term_meta[custom_term_meta]"><?php _e( 'Example meta field', 'yourtheme' ); ?></label></th>
            <td>
                <input type="text" name="term_meta[custom_term_meta]" id="term_meta[custom_term_meta]" value="<?php echo esc_attr( $term_meta['custom_term_meta'] ) ? esc_attr( $term_meta['custom_term_meta'] ) : ''; ?>">
                <p class="description"><?php _e( 'Enter a value for this field','yourtheme' ); ?></p>
            </td>
        </tr>
    <?php
    }
    add_action( 'series_edit_form_fields', 'lx_taxonomy_edit_meta_field', 10, 2 );

    // Save extra taxonomy fields callback function.
    function lx_save_taxonomy_custom_meta( $term_id ) {
        if ( isset( $_POST['term_meta'] ) ) {
            $t_id = $term_id;
            $term_meta = get_option( "taxonomy_$t_id" );
            $cat_keys = array_keys( $_POST['term_meta'] );
            foreach ( $cat_keys as $key ) {
                if ( isset ( $_POST['term_meta'][$key] ) ) {
                    $term_meta[$key] = $_POST['term_meta'][$key];
                }
            }
            // Save the option array.
            update_option( "taxonomy_$t_id", $term_meta );
        }
    }  
    add_action( 'edited_series', 'lx_save_taxonomy_custom_meta', 10, 2 );  
    add_action( 'create_series', 'lx_save_taxonomy_custom_meta', 10, 2 );
    
?>