react native upload file form data - asp.net

Question

it is work fine on post man so i copy the whole code from post mane
formdata.append("file_1", fileInput.files[0], "file.pdf");
and i change fileInput.files[0]to response from react native document picker
my problem i am getting an error on line 166 and this is below back end side code
this code built the .net
line 166 attachments.Add(new OpportunityAttachmentInfo()
{
ContentType = file.ContentType,
FileData = content,
FileName = fileDate.FileName +
file.FileName.Substring(file.FileName.LastIndexOf(".")),
AttachmentTypeId = request[i].AttachmentTypeId,
});
}
this is my react native code
uploadFIle = async (res) => {
var myHeaders = new Headers();
myHeaders.append('Authorization', 'Bearer ' + this.props.accessToken);
var formdata = new FormData();
formdata.append('file', res, res.name);
formdata.append(
'data',
JSON.stringify({
****
}),
);
var requestOptions = {
method: 'POST',
headers: myHeaders,
body: formdata,
redirect: 'follow',
};
fetch(
'https://****',
requestOptions,
)
.then((response) => response.text())
.then((result) => {
console.log('result', result);
this.apiGetSupplierItem();
})
.catch((error) => console.log('error', error));
};