Invoice not sent to customer, nor to dropbox

Hi, it seems everything is in the right place within Woocommerce PDF invoices, but the customer doesn’t receive the invoice after buying and paying. Is there some tiny (perhaps to obvious) thing that easily could be missed? 2 options I could think of:

1. tab ’email’, every line has a checkmark, except for the line ‘invoice for client’. There is no possibility to put a checkmark either.
2. In the product environment the system says ‘waiting for payment’, but Sisow already approved the payment. Something missing in this area? The invoice isn’t sent to my dropbox via emailitin either…

Could you please give me a hint or two to get it solved?

Thanks a lot, Mariska