fix (pos closing entry): validation for 100 pc discount on pos invoic…

…e (backport #44899) (#44930)

fix (pos closing entry): validation for 100 pc discount on pos invoice (#44899)

(cherry picked from commit cfcc24a)

Co-authored-by: Diptanil Saha <50792171+diptanilsaha@users.noreply.github.com>

erpnext/accounts/doctype/sales_invoice/sales_invoice.py

@@ -507,7 +507,7 @@ def validate_pos_return(self):
 				frappe.throw(_("Total payments amount can't be greater than {}").format(-invoice_total))
 
 	def validate_pos_paid_amount(self):
-		if len(self.payments) == 0 and self.is_pos:
+		if len(self.payments) == 0 and self.is_pos and flt(self.grand_total) > 0:
 			frappe.throw(_("At least one mode of payment is required for POS invoice."))
 
 	def check_if_consolidated_invoice(self):