WP Query | search by sub-categories

I have a small problem with the functioning of a search bar that gives the user the possibility to find professionals based on their job categories.

I explain: I am talking about a portal that allows the user to be able to carry out a search as written above.

How I managed the programming: if it is a portal where there are professionals, I created the custom post type: Pro

To specify the services that these professionals are able to perform, I created a plugin that allows me by specifying in the array which custom post types to grant the possibility to implement taxonomies:

register_taxonomy( 'categoria', array( 'pro' ), $args );

now very simply I have implemented a form on a page:

<div id="search_video"  class="container-fluid">
    <div style="text-align: center;background-color: #fff;" class="col-md-12">
        <form name="NOME_FORM" method="get" id="advanced-searchform" role="search" action="<?php echo esc_url( home_url( '/results' ) ); ?>">
            <div class="input-group mb-3">
                <div class="input-group-prepend">
                    <span class="input-group-text"><i class="fa fa-search"></i></span>
                <input type="text" id="art" name="art" class="form-control">

pointing to the results page.

to display the results I used this query:

<?php $art_p = $_GET('art');
        $query_v = array(
            'post_type' => array('pro'),
            'posts_per_page'    => -1,
            'orderby' => 'meta_value',
            'order' => 'ASC',
            'tax_query' => array(
                    'taxonomy' => 'categoria',
                    'terms' => $art_p,
        $res_v = new WP_Query( $query_v );

now the problem:

I have implemented two test professional profiles, in the services category, I have specified as a sub-category of services for professional A:

and for professional B:

but if I look in the website creation bar: it gives me both professionals as a result and this is not good.

So my question is how can I filter the results so that the user search is based on the sub-category of services and only brings out the professionals who own that sub-category, what did I do wrong with my query?