I am sorry for this, I thought you are talking about PPOM. To use inline checkout please request 2checkout support to enable Inline 2Checkout. That’s how they have written in docs. They will enable inline checkout support against your account in few hours.
I clicked above link and I have redirected to order received page, and when you redirected from 2checkout it has some parameters which finalize the order, there is not such error like ‘-1’