"can" is happening now. It is present tense. "could" is used here in the conditional tense, which means it could be past, present or future, really anytime this happens. "if" statements usually use the conditional for this reason.
I keep getting "Almost correct!" when I use the words logon or login for ensaluti. Both are acceptable (UK) English words, though the past tense of the verb to logon is logged on, so I can see where Duo is coming from.