Missed utterances
The most common error will be when utterances aren't understood or aren't what the chatbot expected. This can be because the user typed something incorrectly, misspelled a word, or just typed a response you hadn't thought of. Alexa and Lex both use natural language understanding (NLU) to try to reduce the errors from misspelling and varied responses but they aren't perfect.
Because not understanding the user's utterance is such a common error, both Lex and Alexa also have systems to handle them. This involves a failure phrase that can be sent to the user when the chatbot doesn't understand what the user just said. Make sure that this is set up properly and that you are asking the user to try again or to choose a different option:
Alexa and Lex also have a feature that stores all of the times that it couldn't understand an utterance. Using this list, you can add more sample utterances to help the chatbot understand more. Doing this regularly can give a massive boost to your user satisfaction, as well as helping you understand how your users interact with your bot.