There is a closed issue at github, regarding the payment of expenses.
https://github.com/odoo/odoo/issues/8648
It refers to a video in youtube, where it says this is the way to register expenses payments:
https://github.com/odoo/odoo/issues/8648
Following step by step, paying in cash, or paying with bank, there is the same thing. The payment is not made, and the expense remains "waiting for payment".
There is a confuse stuff, related to the fact that in the statement, you will find a reconcile button. It seems to make the reconcilation, but after that, there is a new button inviting you to "validate".
Why the expenses app offers you to reconcile something if it not still validated?
Why the expense is not being register as payed, even after all these steps?
Where can I see the reconciled entries?
