Ajax call when not logged in, get_terms return empty array

hello! I’ve got a strange problem.
I have two html list, when i choose a region, it sends an ajax request to wordpress and returns the list of this region’s province.
The problem is that the get_terms() function of wordpress doesn’t retrieve any province when we are not logged in, even if he correctly received the data. The value $_POST[‘region’] is correct even if you’re not connected.

I may have made some mistakes, i’m french and i apologize.

Here is the code, hope someone can help me.

<?php
	/*
	Plugin Name: Ajax Départements
	Description: Récupère les sous categories(départements) d'une categorie(région)
	Version: 0.1
	Author: EnessFr
	*/

	//Enregstrement du trigger et du callback
	add_action( 'wp_ajax_dpt-ajax-request', 'ajaxGetDepartement' );
	add_action( 'wp_ajax_nopriv_dpt-ajax-request', 'ajaxGetDepartement' );

	//insertion du script
	wp_enqueue_script( 'dpt-ajax-request', plugin_dir_url( __FILE__ ) . 'ajax.js', array( 'jquery' ), null, true );

	//Enregistrement de l'url ajax
	wp_localize_script( 'dpt-ajax-request', 'dptAjaxRequest', array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ) );

	//callback ajax
	function ajaxGetDepartement(){
	$departements = null;
	$regionToExclude = array();
	$tmpRegionName = $_POST['region'];

	//Récupération des régions parents
	$regionsParents = get_terms('category',array(
		'parent' => 0,
		'hide_empty' => false,
		));

	foreach($regionsParents as $rg){
		array_push($regionToExclude, $rg->term_id);
	}
	array_push($regionToExclude, 1); // 1 = catégorie non-classé

	//Récupération de la région passée en arguments
	if(strval($_POST['region']) != 'wqsftaxoall'){ // une région valable est re?us
		$tmpRegion = get_terms('category',array(
			'slug' => $tmpRegionName,
			'hide_empty' => false,
			)
		);

		$regionParent = $tmpRegion[0]->term_id;

		//Récupération des départements
		$departements = get_terms('category',array(
			'child_of' => $regionParent,
			'hide_empty' => false,
			'orderby' => 'name',
			'order' => 'ASC',
			'exclude' => $regionToExclude,
			));
	}else{ //récupération de tous les départements

		//Récupération des départements
		$departements = get_terms('category',array(
			'hide_empty' => false,
			'orderby' => 'name',
			'order' => 'ASC',
			'exclude' => $regionToExclude,
			));

	}

	//Construction et affichage des résultats
	$options = '<option selected value="wqsftaxoall">Tous les départements</option>';

	foreach($departements as $dpt){
		$options .= '<option value="'.$dpt->slug.'">'.$dpt->name.'</option>';
	}

	echo $options;
	die();
	}

	?>