Originally Posted by joony

Since you're being offered $550 + 20k miles, you're probably actually on a W or S/T/K/L/G/N fare according to the award chart: http://www.united.com/web/en-US/cont...2012-03-03.pdf

GPU - "They can be used on all paid, published fares except Z, P, S, T, K, L, G and N fare classes"

Hopefully you're on that W fare so you can use the GPU.