I get this error with some invoices whenever i try to send it to ZATCA when i click on the button process now on the header of the form

here's the error

  File "/home/odoo/src/odoo/odoo/addons/base/models/ir_http.py", line 242, in _dispatch
    result = request.dispatch()
  File "/home/odoo/src/odoo/odoo/http.py", line 702, in dispatch
    result = self._call_function(**self.params)
  File "/home/odoo/src/odoo/odoo/http.py", line 368, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/service/model.py", line 94, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/http.py", line 357, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 925, in __call__
    return self.method(*args, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 546, in response_wrap
    response = f(*args, **kw)
  File "/home/odoo/src/odoo/addons/web/controllers/main.py", line 1328, in call_button
    action = self._call_kw(model, method, args, kwargs)
  File "/home/odoo/src/odoo/addons/web/controllers/main.py", line 1316, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/odoo/src/odoo/odoo/api.py", line 471, in call_kw
    result = _call_kw_multi(method, model, args, kwargs)
  File "/home/odoo/src/odoo/odoo/api.py", line 456, in _call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/home/odoo/src/odoo/addons/account_edi/models/account_move.py", line 680, in button_process_edi_web_services
    self.action_process_edi_web_services(with_commit=False)
  File "/home/odoo/src/odoo/addons/account_edi/models/account_move.py", line 684, in action_process_edi_web_services
    docs._process_documents_web_services(with_commit=with_commit)
  File "/home/odoo/src/odoo/addons/account_edi/models/account_edi_document.py", line 254, in _process_documents_web_services
    self._process_job(documents, doc_type)
  File "/home/odoo/src/odoo/addons/account_edi/models/account_edi_document.py", line 203, in _process_job
    edi_result = edi_format._post_invoice_edi(invoices)
  File "/home/odoo/src/odoo/addons/l10n_sa_edi/models/account_edi_format.py", line 455, in _post_invoice_edi
    return {invoice: self._l10n_sa_post_zatca_edi(invoice)}
  File "/home/odoo/src/odoo/addons/l10n_sa_edi/models/account_edi_format.py", line 334, in _l10n_sa_post_zatca_edi
    response_data, submitted_xml = self._l10n_sa_export_zatca_invoice(invoice, xml_content)
  File "/home/odoo/src/odoo/addons/l10n_sa_edi/models/account_edi_format.py", line 238, in _l10n_sa_export_zatca_invoice
    signed_xml = self._l10n_sa_get_signed_xml(invoice, unsigned_xml, x509_cert)
  File "/home/odoo/src/odoo/addons/l10n_sa_edi/models/account_edi_format.py", line 210, in _l10n_sa_get_signed_xml
    signed_xml = self._l10n_sa_sign_xml(unsigned_xml, x509_cert, invoice.l10n_sa_invoice_signature)
  File "/home/odoo/src/odoo/addons/l10n_sa_edi/models/account_edi_format.py", line 79, in _l10n_sa_sign_xml
    root = etree.fromstring(xml_content)
  File "src/lxml/etree.pyx", line 3252, in lxml.etree.fromstring
  File "src/lxml/parser.pxi", line 1912, in lxml.etree._parseMemoryDocument
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/odoo/src/odoo/odoo/http.py", line 658, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/odoo/src/odoo/odoo/http.py", line 301, in _handle_exception
    raise exception.with_traceback(None) from new_cause
ValueError: can only parse strings

don't appear on all invoices but i can't get the difference why i have that error on some invoices and others work fine