Account Statement: some invoice payments already paid manually

I opened some of the supplier invoices and clicked the “Pay” button

Now I would like to try the account_statement module.

All the invoice lines appear on the “Origin” tab

Nothing appears on the “Statement Lines” tab

Can I tell it that some of the “Origin” lines are the same as payments already executed?

No you should never use the “Pay” button if you are using the statement.

If I manually process payments for all the remaining lines, will I be able to use the statement module for future months?

I guess. The problem comes from mixing both methods because in such case you can not be sure what was manually processed when entering the statement. So over a specific period, you must use only one method.