Metabox for custom post type with termmeta saving

I’m trying to create a metabox for my custom post type: pro, which saves the information not in the postmeta table but in termmeta, I share the structure but does not save any data in the termmeta table, where am I wrong?

<?php

add_action( 'add_meta_boxes', 'AMC_servizio_uno' );
function AMC_servizio_uno() {
    add_meta_box(
        'AMC_metabox_servizio_uno',         /*ID DELLA METABOX*/
        'Servizio uno',        /*TITOLO DELLA METABOX*/
        'plugin_add_custom_box',        /*CALLBACK DELLA METABOX*/
        'pro',                     /*TIPO DI POST CHE VOGLIAMO A CUI VENGA APPLICATA LA METABOX*/
        'side',                             /*POSIZIONE DELLA METABOX:*/
        'default' );                        /*PRIORITA' DELLA METABOX*/

}

// Print the meta box
add_action( 'servizi_pro_edit_form', 'plugin_add_custom_box' );
function plugin_add_custom_box( $term ) {
    $value = get_term_meta( $term->term_id, 'plugin_meta_key', true );
    ?>
    <label for="plugin_meta_key">Description of the field: </label>
    <input name="plugin_meta_key" type="text" value="<?php echo $value; ?>">
    <?php
}

// Save the meta value
add_action( 'edit_term', 'plugin_save_term_meta' );
function plugin_save_term_meta( $term_id ) {
    if ( array_key_exists( 'plugin_meta_key', $_POST ) ) {
        update_term_meta(
            $term_id,
            'plugin_meta_key',
            sanitize_text_field( $_POST['plugin_meta_key'] )
        );
    }
}

how can I do?