to think wrongly that sb / sth is sb / sth else; to change the order or arrangement of a group of things, especially by mistake or in a way that you do not want
mix sb / sth up (with sb / sth)
to think wrongly that sb / sth is sb / sth else
I think you must be mixing me up with someone else.
mix sth up
to change the order or arrangement of a group of things, especially by mistake or in a way that you do not want
Someone has mixed up all the application forms.
Definiciones del Oxford Advanced Learner's Dictionary, 9.ª edición