"mark paid" stays unpaid

[keneso]

Hi,

 

I had setup an hidden product, and made an order, on the invoice page it would show free product, then I changed the payment method, and set it for that order as well (don't ask me why ...), and now it shows the order as unpaid. I select it, and click "mark paid", and it brings me to the invoice list, leaving it unpaid.

 

Any suggestions?

 

Thank you