Flexi can automatically create a warehouse document for every invoice (an issue note for an outgoing invoice, a receipt note for an incoming invoice) without any manual intervention. This is configured on the document type, so the setting applies to all newly issued invoices of that type.
Issued Invoices
Open Sales → Document Types → Issued Invoice Types.
In the record detail, on the Invoice tab, check Automatically generate warehouse documents and require serial number entry.
Save using the Save and Close button.
Received Invoices
Open Purchase → Document Types → Received Invoice Types.
In the record detail, on the Invoice tab, check Automatically generate warehouse documents and require serial number entry.
Save using the Save and Close button.
⚠️ This flag also enables requiring serial numbers for items that have them tracked. The setting takes effect only for newly issued invoices and does not affect existing documents.