Error sent invoice by email

The system generates the invoice in pdf but it does not send me by mail,
I can’t find any log with the error
I have configured the smtp server and when performing the test if I receive the mail
Could you guide me where I should look to find the fault?
thanks

have you approved this invoice?

it is not approved
Does it need to be approved before the system sends it?
what is the correct procedure?

it is described in documentation. https://yeti-switch.org/docs/en/web-interface/yeti-ui-billing/yeti-ui-billing-invoices.html