"Is there money?"
The use of は is pointing to the fact that "money" is the topic of the sentence, as in "(On the subject of) money, is there any?" が could instead be construed as "Do you have money?" or similar
From what I read from other comments: は is used for marking the topic, of something that is already established, and が does the same but expresses a new idea, or adds new information. In this case money is something that is well established, while things like emotions and tastes require が.
This sentence doesn't seem to fit any of the exceptions to the rule of があります. https://www.learn-japanese-adventure.com/arimasu-imasu-existence.html
Duolingo needs to ease up on how strict they are with particles. If I was having a regular conversation with a friend I wouldn't use a particle at all. So i t.f s not wrong to omit them. If I use the wrong one that's one thing.