Unsure about your question, never have I had problems there...

In my experience, Ibis / Ibis Style included, reception staff have been pretty responsive to reasonable requests. In my experience redeeming one voucher has been done pretty swiftly, even though it includes exchange rate conversion, burning the voucher, having it applied towards the room bill, etc. On the other hand if a batch of vouchers needs to be converted then a large amount of time is required and one is better off leaving them do their job on their schedule, without further pressure.

Thus, I assume, having a stay credit on the spot towards an account should also be pretty swift, obvious, if done by someone minimally experienced with the system and on an exception basis, where we fear a problem may arise.