If you are answering the question correctly but the Musiah app is telling you that your answer is incorrect, this issue is almost always due to a fault with your MIDI keyboard. This particular keyboard fault is quite common in the poorer quality keyboard brands such as "Base" or "Meike". (Please avoid these brands as they are dreadful).
The only time it might not be a keyboard fault is if you have a very fancy / high-end keyboard with lots of customizable settings, in which case it could be a setting on the keyboard. In this case, try to disable any unnecessary extra layers/pads on your keyboard (you'll need to consult your keyboard manual). Alternatively, if the keyboard manual is available online, we are happy have a look at it to see if we can figure out whether it is in fact a setting that needs to be changed.
In summary, the issue is that the keyboard is sending out two MIDI messages for each note played (it is only supposed to send out one MIDI message for each note played). So, in a question where the answer is just a single note (e.g. play Middle C) the keyboard will appear to work fine. This is because, in a single note question, once the Musiah app has received the correct note, it then stops listening. So if an extra note is played (or the same note is played twice), this is generally not an issue.
But in a question such as play all 5 C's on the keyboard (where the answer is a sequence of notes), because of the fault in the keyboard, the Musiah app receives the two MIDI messages from the keyboard when you play the first note, and the app thinks that you are playing the first note twice (which of course you are not).
Realistically, if your keyboard is one of the cheap/poor quality ones and you are having this issue, your only option is to purchase another keyboard. Our Keyboard Info page describes what to look for when choosing a MIDI keyboard.