upload attachment to Zoho books bill from Zoho CRM

upload attachment to Zoho books bill from Zoho CRM

Hello

I have a document stored in a file field in CRM (module reservation)
I am trying to attach this document to the bill created in Zbooks using Deluge, but I keep having issue, either File is empty or {"code":2,"message":"The request passed is not valid."
Please see below the function written. Any help would be really nice!

Org = "XXXX";
resaID = 1111111111;
ResaDetails = zoho.crm.getRecordById("Reservations1",resaID);
Invoice_crm = ResaDetails.get("Invoice");
attachment_Id = Invoice_crm.getjson("attachment_Id");

//test invoice Zbooks to which file must be attached
IDinvoice_Zbooks = 222222222222;

download_inv_File = invokeurl
[
url :"https://www.zohoapis.com/crm/v2/Reservations1/" + resaID + "/Attachments/" + attachment_Id
type :GET
connection:"zohoauth"
];
files = list();
download_inv_File.setParamName("file");
files.add(download_inv_File);

Upload_file_Zbooks = invokeurl
[
url :"https://books.zoho.com/api/v3/bills/" + IDinvoice_Zbooks + "/attachment?organization_id=" + Org
type :POST
files : files
connection:"zbooksall"
];
info Upload_file_Zbooks;