Hi Tracey,
You do have the option to add multiple attachments to an email within KashFlow using the paperclip option. The reason we only auto populate one invoice is because that then credits an audit trail within the system for that invoice. Allowing you to add others to that email would not record this.
If we do get plenty of votes for the feature we can certainly look into making a change.
Send mulitple invoices in ONE email
Merged