maybe ???

backend/src/main/resources/get/cesare.js

@@ -23,7 +23,7 @@ async function decrypt() {
             method: "POST", headers: { "Content-Type": "application/json" },
             body: JSON.stringify({ ciphertext: ciphertext })
         });
-        document.getElementById("decodedtext").value = await res.text();
+        document.getElementById("decodedtext").value = await res.JSON;
     } catch (e) { alert("Errore di connessione!"); }
 }