Hi Everyone,
I’ve noticed that if the “Generate the invoice number for draft invoices” is set to no and an invoice is saved and use the send email option, no invoice number is visible on the email as well as on the PDF file. But after sending the email, the invoice is marked as sent. However, changing invoice status to sent prior to sending email does seems to work along with the “Generate the invoice number for draft invoices” option set to yes. So it seems like the send email function is failed to generate an invoice number prior to sending the actual invoice email.