Zoho Desk API: set timeEntry.invoiceId = "" (null) [remove connection between ticket timeentry and books invoice]

Zoho Desk API: set timeEntry.invoiceId = "" (null) [remove connection between ticket timeentry and books invoice]

Hi all,

I would like to link time entries with invoices in Books via API. In doing so, I made a wrong connection, unfortunately I can no longer remove the InvoiceId! Very bad. :( How can I remove the link? Please help me, many thanks in advance!

Deluge:
  1. params = Map();
  2. params.put("invoiceId", "");
  3. test = invokeurl
  4. [
  5.      url :"https://desk.zoho.eu/api/v1/tickets/xxxxxxxxxxxxxxxx/timeEntry/xxxxxxxxxxxxxxxx"
  6.      type :PATCH
  7.      parameters:params.toString()
  8.      connection:"zohodesk"
  9. ];
  10. info test;
Result:

{"errorCode":"UNPROCESSABLE_ENTITY","message":"The server was unable to process the data you entered."}