Can't send sms on new purchase order

I tried to use inbuilt sms notification feature in v13 to send sms to supplier after submission of PO from the system with summary of order as well.
I wrote a jinja code and it renders well. No problem with that.

But I can’t manage to send sms to the supplier. Supplier is created well with a valid mobile num as well. But every time I save a new PO, it says “Please enter valid mobile nos”.
SMS settings are well defined.

The following is the error log:

Traceback (most recent call last):
  File "apps/frappe/frappe/email/doctype/notification/", line 134, in send
    self.send_sms(doc, context)
  File "apps/frappe/frappe/email/doctype/notification/", line 245, in send_sms
  File "apps/frappe/frappe/core/doctype/sms_settings/", line 56, in send_sms
    receiver_list = validate_receiver_nos(receiver_list)
  File "apps/frappe/frappe/core/doctype/sms_settings/", line 31, in validate_receiver_nos
    throw(_("Please enter valid mobile nos"))
  File "apps/frappe/frappe/", line 439, in throw
    msgprint(msg, raise_exception=exc, title=title, indicator='red', is_minimizable=is_minimizable, wide=wide, as_list=as_list)
  File "apps/frappe/frappe/", line 418, in msgprint
  File "apps/frappe/frappe/", line 372, in _raise_exception
    raise raise_exception(msg)
frappe.exceptions.ValidationError: Please enter valid mobile nos

Is there a solution for this matter yet?

it happened when ever I am trying to make an auto notification with SMS channel with different DocType (payment entry - sales invoice - …)

same message appear every time
“Please enter valid mobile nos”

even though all SMS Settings are correct and I can send SMS message from SMS Center as I add one Mobile number or more.

I guess the matter is to do the selection of Mobile number of the costumer or the supplier.