Seemed to have fixed it

packages/frontend/src/os.ts

@@ -107,12 +107,19 @@ export function promiseDialog<T extends Promise<any>>(
 		showing.value = false;
 		if (onFailure) {
 			onFailure(err);
+		} else {
+			if (err.message) {
+				alert({
+					type: 'error',
+					text: err.message,
+				});
 			} else {
 				alert({
 					type: 'error',
 					text: err,
 				});
 			}
+		}
 	});
 
 	// NOTE: dynamic importすると挙動がおかしくなる(showingの変更が伝播しない)