WP-API missing data for menu location

WP-API doesn’t show any data for the registered custom menu location.

// url/wp-json/wp/v2/menu-locations/nav-menu1
{
code: "rest_no_route",
message: "No route was found matching the URL and request method",
data: {
status: 404
}
}

// the plugin function.php
//
function mswp_register_menus(){

	$theme_locations = get_option( MSWP_THEME_LOC_OPTION );

	if( $theme_locations ){
		foreach( $theme_locations as $loc ){
			register_nav_menus( array(
				$loc['slug'] => $loc['name']
			) );
		}
	}
}
add_action( 'init', 'mswp_register_menus' , 20 );