Field name for purchase order number - using {{naming_series}} didn’t give numerals

I need the field name to show the purchase order number in my custom email template’s subject line, using {{naming_series}} didn’t give numerals

I confirm it’s naming_series
check table from backend

It only gives the following data PO/ABC/ there should be numerals after this that dies not reflect.
I have put custom naming series as PO/ABC/ is that the issue or should i make the custom naming series as PO/ABC/#####

Try {{ name }} instead and check.

If you check doctype field name is naming_series, is thete a methode to find the same