How to query for exact string in custom field?

I have a custom field which I set in a var

$customCoords = usp_get_meta(false, 'usp-custom-90');

That custom field has a string like this:

45.46135436613811,9.175124650000043

Then I get some values from a form:

$lat = $_GET['usp-custom-19'];
$ln = $_GET['usp-custom-20'];

And I join them like this:

$coordinates = $ln . "," .$lat;

Now $coordinates is a string like this:

45.46135436613811,9.175124650000043

And now I want to query all posts which have the same exact string as $coornidates and I do

$args = get_posts( 
    array( 
        'post_type'      => 'post', 
        'posts_per_page' => -1, 
        'meta_query'     => array(
            array(
                'key'     => $customCoords,
                'value'   => $coordinates,
                'compare' => '=',
                'type' => 'CHAR'
            )
        ) 
    ) 
);
$query = new WP_Query( $args );
if ( $query->have_posts() ) {
    while ( $query->have_posts() ) {
        $query->the_post();
        echo the_title(); 
        echo "<br>";
    }
}

But I get nothing.

UPDATE

$lat = $_GET['usp-custom-19'];
$ln = $_GET['usp-custom-20'];

$args = get_posts( 
    array( 
        'post_type'      => 'post', 
        'posts_per_page' => -1, 
    ) 
);
$query = new WP_Query( $args );
if ( $query->have_posts() ) {
    while ( $query->have_posts() ) {
        $query->the_post();
        $customCoords = usp_get_meta(false, 'usp-custom-90');
        $arrayCoords = explode( ",", $customCoords );
        $radiusLn = +$arrayCoords[0] + 10;
        $radiusLat = +$arrayCoords[1] + 10;
        $args = array(
            'post_type' => 'post',
            'meta_query' => array(
                array(
                    'relation' => 'AND',
                    array(
                        'key' => 'get_usp-custom-19',
                        'value' => array($ln, $radiusLn),
                        'compare' => '>='
                    ),
                    array(
                        'key' => 'get_usp-custom-20',
                        'value' => array($lat, $radiusLat),
                        'compare' => '<='
                    ),
                ),
            ),
        );
        $query = new WP_Query( $args );
        if ( $query->have_posts() ) {
            while ( $query->have_posts() ) {
                $query->the_post();
                the_title();
            }
        }
    }
}