wip found how to theorically get ajax request in php but for the moment i get error 400

plugins/wp_model_plugin/js/menu/menu.js

@@ -0,0 +1,18 @@
+const inputElement = document.getElementById('mytext');
+const sendButton = document.getElementById('mybutton');
+
+sendButton.addEventListener('click', () => {
+	const inputValue = inputElement.value;
+	const myurl = php_data.ajax_url;
+	console.log(myurl);
+
+	fetch(myurl, {
+		method: 'POST',
+		credentials: 'same-origin',
+		body: JSON.stringify({
+			action: 'get_data',
+			_ajax_nonce: php_data.nonce,
+			data: inputValue,
+		})
+	})
+});