Underpaid? That looks like a shitload of gold coins to me considering he can't handle simple tasks. Then again, gold is ridiculously undervalued in these kind of video game-inspired fantasy settings so maybe he is being underpaid.
He's disappointed because it's a bag full of uninteresting yellow discs, when he was expecting gummies. In the last panel of the page before he opens the bag he's holding it and imagining the winking gummy.
He also needs this lesson https://www.youtube.com/watch?v=dgct3Jn8pFA
@Wexmajor I always find it weird when something decides that its currency is simply gold and something like a beer costs 50 gold coins or something as if gold coins were small change.