fix: subscription prepaid date validation (#24356)

diff --git a/erpnext/accounts/doctype/subscription/subscription.py b/erpnext/accounts/doctype/subscription/subscription.py
index 552a5d4..e023b47 100644
--- a/erpnext/accounts/doctype/subscription/subscription.py
+++ b/erpnext/accounts/doctype/subscription/subscription.py
@@ -446,7 +446,7 @@
 		if not self.generate_invoice_at_period_start:
 			return False
 
-		if self.is_new_subscription():
+		if self.is_new_subscription() and getdate() >= getdate(self.current_invoice_start):
 			return True
 
 		# Check invoice dates and make sure it doesn't have outstanding invoices