Timatic states as USA passport/citizen you can get VOA in Laos but need outbound documentation-
https://www.united.com/web/en-US/app...aspx?i=TIMATIC
I agree with Often1 in you would not be able to successfully dispute the charge.
The easiest way is to book an award flight in the future (within allowable limits) and then cancel the ticket after arrival in Laos.