Uploading file using PERN stack - reactjs

Question

I'm using PERN stack and while uploading the files in the UI except the xlsx file each files are getting uploaded. I have no what's going wrong. I referred a lot of things but none of them are targeting to what I'm looking for.
I'm even providing the code.
const data = new FormData();
console.log("state in general =====", this.state.selectedFile);
if (selectedFile && selectedFile.length > 0) {
for (var x = 0; x < selectedFile.length; x++) {
data.append("file", selectedFile[x]);
data.append("filename[]", this.state.selectedFile[x].name);
}
console.log("uploaded file data", data); // this data variable is my payload in the api.
}
Backend error :
Backend code :
await Promise.all(
req.files.map(async file => {
let document = await someClass.select("tableName", {
//few parameters.
});
console.log(document);
if (document.length === 0) {
// if the file doesn't exists then only upload the new file.
insert.then(doc => {
const result = {
status: "ok",
filename: doc.filename,
message: "Upload Successfully!",
};
messages.push(result);
})
.catch(err => {
console.log("error in uploading file----------", err);
const result = {
status: "fail",
filename: file.originalname,
message: "Can NOT upload Successfully",
};
sendResponse(res, "Files Found", result);
});
} else {
// sendResponse(res, "Files found", document);
}
})
);
Any help will be appreciated.