how to post attachments using Upload Collection - pending - sapui5

Question

I am trying to use the same code wrt official upload collection pending
and in controller where upload is called :
onStartUpload: function(oEvent) {
var oUploadCollection = this.byId("UploadCollection");
var cFiles = oUploadCollection.getItems().length;
var uploadInfo = cFiles + " file(s)";
if (cFiles > 0) {
oUploadCollection.upload();
MessageBox.information("Uploaded " + uploadInfo);
}
},
I have set all required header parameters in onChange as:
onChange: function(oEvent) {
var oUploadCollection = oEvent.getSource();
// Header Token
var oCustomerHeaderEmailToken = new UploadCollectionParameter({
name: "xxxx",
value: xxxxx
});
// Header Token
var oCustomerHeaderAuthToken = new UploadCollectionParameter({
name: "xxxx",
value: "xxxx"
});
oUploadCollection.addHeaderParameter(oCustomerHeaderEmailToken);
oUploadCollection.addHeaderParameter(oCustomerHeaderAuthToken);
},
When i tried uploading in BE it gave me error as :
current request is not a multipart request
Then I tried adding to onChange :
var oCustomerHeaderContentType = new UploadCollectionParameter({
name: "Content-Type",
value: "multipart/form-data; boundary=----WebKitFormBoundarycXEQN6de4OdX0FBe"
});
oUploadCollection.addHeaderParameter(oCustomerHeaderContentType);
It didn't work even though the error is gone ,
The API works fine and tested in postman but why not with upload collection ? May i know the request sent is a multipart form-data ? Do I need to add any extra parameters ?
How does a simple back end API (if JAVA/Python) would be to collect files from when upload collection is used ? as there is no name to refer in server side like fileuploader and if the request is a multipart in upload collection
hope the experts help me out with this ... thanks :)