Starbucks lets you place an order using Alexa with the Starbucks Reorder skill. After you enable the skill, you will need to link your account. The skill will not work unless you've previously placed a mobile order with the Starbucks app on Android or iOS. It can place an order at one of the last 10 Starbucks locations you've visited in person. You can also check your account balance and switch between your five previous mobile orders. 
Like all AI devices that use National Language Processing or NLP, Alexa does not understand all voices easily. But she learns to understand her people over time. She does, however, require people to speak in simple terms, with appropriate pauses, and use specific word orders. There are many times when she will say "I'm sorry, I don't know the answer to that question." More than likely, she doesn't recognize a word order or misunderstood the question.