I have set this up: WordPress Dashboard > WooCommerce > Settings > Booster > PDF INVOICING & PACKING SLIPS > Email Options.
In the Email Options
Credit invoice/nota Attach PDF to emails: Refunded order
And:
I have set this up: WordPress Dashboard > WooCommerce > Settings > Booster > PDF INVOICING & PACKING SLIPS > General.
In PDF Billing Module Options:
Credit invoice/nota Attach PDF to emails: Create at order status Refunded
So when I change the order status to Refunded a credit invoice/Nota is made, but it is not added to the Refunded order mail that has been sent.