React Native && Node js How to upload image - node.js

Question

I am having trouble uploading an image from my react native app. I have a react app that uploads images to the backend from camera as a file.
let pic = await camera.current.takePictureAsync({
quality: 1,
base64: true,
});
setPicture(pic);
Then
onPress={() => {
const formData = new FormData();
formData.append("file", {
name: picture + "",
type: picture.type,
uri:
Platform.OS === "ios"
? picture.uri.replace("file://", "")
: picture.uri,
});
console.log(formData);
httpClient
.post("demo/testsaveimg", formData)
.then((request) => {
if (request.data == "ok") {
console.log(request.data);
}
});
}}
This is my Formdata to service
and then, here is my service
app.post('/testsaveimg', async function (req, res, next) {
let storageUploadFile = multer.diskStorage({
destination: (req, file, next) => {
const folder = './test/'
if (!fs.existsSync(folder)) {
fs.mkdirSync(folder)
}
next(null, folder)
},
filename: (req, file, next) => {
const ext = file.mimetype.slice("/")[1]
next(null, `${file.fieldname}-${Date.now()}.${ext}`)
}
})
let UploadFile = multer({ storage: storageUploadFile }).single("files");
UploadFile(req, res, async function (err) {
console.log(req.file);
if (err instanceof multer.MulterError) {
return res.status(500).json(err);
} else if (err) {
console.log(99);
return res.status(500).json(err);
}
if (req.file != undefined) {
console.log("ok");
res.json("ok")
} else {
console.log("no");
res.json("no")
}
})
})
But there are no pictures in the folder "./test/" and response is "no"
that means "req.file = undefined"
What steps am I doing wrong?
or is there another way to write?