Hello Kaveh,
Hope you're doing well.
Regarding the issue with invoices getting expired, please note that invoices are set to expire if the payment fails and remains unpaid for a specific number of days. You can customize the number of days by going to Settings, then selecting Global Settings, and finally adjusting the "Expiration of Invoice" setting.
If you wish to prevent such invoices from expiring, you have the flexibility to modify the number of days from that section according to your requirements.
Furthermore, I would like to inform you that if you are utilizing the dunning management feature in Pabbly Subscription Billing, invoice expiration occurs once the dunning process concludes and the invoice remains unpaid.
I hope this clarifies the matter. Should you have any further questions or concerns, please feel free to reach out.