Error 1872: The document has no document element. at line -1 when export xml from copernicus plugin ojs

Describe the issue or problem
when i click validate file, in export plugin to copernicus in ojs ive got this error
Error 1872: The document has no document element. at line -1

Steps I took leading up to the issue
For example:

  1. i goto export impoirt in tools,
  2. then goto oxport import to copernicus
  3. i scrol down to the volume i want to export
  4. when click to validate ive got error

What application are you using?
Current version: 3.2.1.3

Additional information

when i download the file xml