Document Naming Settings with only .## does not apply

I am facing an issue where I am trying to set naming series on brands. when I set .## it gives me below error, what does it means?

App Versions

	"erpnext": "14.70.6",
	"frappe": "14.76.2"


Form/Document Naming Settings/Document Naming Settings


Traceback (most recent call last):
  File "apps/frappe/frappe/", line 97, in application
    response = frappe.api.handle()
  File "apps/frappe/frappe/", line 55, in handle
    return frappe.handler.handle()
  File "apps/frappe/frappe/", line 48, in handle
    data = execute_cmd(cmd)
  File "apps/frappe/frappe/", line 86, in execute_cmd
    return, **frappe.form_dict)
  File "apps/frappe/frappe/", line 1619, in call
    return fn(*args, **newargs)
  File "apps/frappe/frappe/", line 312, in run_doc_method
    response = doc.run_method(method)
  File "apps/frappe/frappe/model/", line 931, in run_method
    out = Document.hook(fn)(self, *args, **kwargs)
  File "apps/frappe/frappe/model/", line 1283, in composer
    return composed(self, method, *args, **kwargs)
  File "apps/frappe/frappe/model/", line 1265, in runner
    add_to_return_value(self, fn(self, *args, **kwargs))
  File "apps/frappe/frappe/model/", line 928, in fn
    return method_object(*args, **kwargs)
  File "apps/frappe/frappe/core/doctype/document_naming_settings/", line 89, in update_series
  File "apps/frappe/frappe/core/doctype/document_naming_settings/", line 148, in check_duplicate
    frappe.throw(_("Series {0} already used in {1}").format(series, existing_series[series]))
KeyError: '.###'

Request Data

	"type": "POST",
	"args": {
		"docs": "{\"name\":\"Document Naming Settings\",\"owner\":\"Administrator\",\"modified\":\"2024-06-12 00:28:47.044039\",\"modified_by\":\"Administrator\",\"docstatus\":0,\"idx\":\"0\",\"user_must_always_select\":0,\"current_value\":0,\"doctype\":\"Document Naming Settings\",\"transaction_type\":\"Brand\",\"__unsaved\":1,\"naming_series_options\":\".###\"}",
		"method": "update_series"
	"freeze": true,
	"headers": {},
	"error_handlers": {},
	"url": "/api/method/run_doc_method"

Response Data

	"exception": "KeyError: '.###'"

Because series is already used for another doctype, so please set the another series and check it.

Check Existing Series: First, verify the existing series in the Document Naming Settings to see if ‘.###’ is indeed being used. You can do this by navigating to the Document Naming Settings

Yes, i do have another series but how can I set the same one?

you can’t use same just add a . (dot) or something else it will work.