Sms alert on leave application

I have tried to set up sms alert on submission of leave application by employee. I have a good and working settings for sms.

I tried the following code through client script.

Doctype: Leave application
Apply to: Form
Enabled: checked on

Script:

frappe.ui.form.on("Leave Application", "after_save", function(frm) {
        var message = 'New Leave Application by ' + [frm.doc.employee_name] + ' FROM ' + frm.doc.from_date + ' TO ' + frm.doc.to_date ;


       frappe.call({
               method: "frappe.core.doctype.sms_settings.sms_settings.send_sms",
               args: {
                   receiver_list: '980000000', // contact number 
                   msg: message,
               },
               callback: function(r) {
                   if (r.exc) {
                       msgprint(r.exc);
                       return;
                   }
               }
             });
})

I get the following error:

AttributeError: ‘int’ object has no attribute ‘replace’

Also this is the error message:

### App Versions
```
{
	"erpnext": "13.18.0",
	"frappe": "13.18.0"
}
```
### Route
```
Form/Leave Application/HR-LAP-2022-00010
```
### Trackeback
```
Traceback (most recent call last):
  File "apps/frappe/frappe/app.py", line 68, in application
    response = frappe.api.handle()
  File "apps/frappe/frappe/api.py", line 55, in handle
    return frappe.handler.handle()
  File "apps/frappe/frappe/handler.py", line 31, in handle
    data = execute_cmd(cmd)
  File "apps/frappe/frappe/handler.py", line 67, in execute_cmd
    return frappe.call(method, **frappe.form_dict)
  File "apps/frappe/frappe/__init__.py", line 1208, in call
    return fn(*args, **newargs)
  File "apps/frappe/frappe/core/doctype/sms_settings/sms_settings.py", line 56, in send_sms
    receiver_list = validate_receiver_nos(receiver_list)
  File "apps/frappe/frappe/core/doctype/sms_settings/sms_settings.py", line 26, in validate_receiver_nos
    d = d.replace(x, '')
AttributeError: 'int' object has no attribute 'replace'

```
### Request Data
```
{
	"type": "POST",
	"args": {
		"receiver_list": "9800000000",
		"msg": "New Leave Application by Test Employee Ttt FROM 2022-03-29 TO 2022-03-29"
	},
	"headers": {},
	"error_handlers": {},
	"url": "/api/method/frappe.core.doctype.sms_settings.sms_settings.send_sms"
}
```
### Response Data
```
{
	"exception": "AttributeError: 'int' object has no attribute 'replace'"
}
```

Also, currently I have tried to hard code the receiver phone number, but I want the sms to go to the assigned leave approver’s num.

Can anyone help me what’s the error in the code.