"Señor, por favor espere acá."
Translation:Sir, please wait here.
Confused as well? Most of the answers I find say aqui and aca are: Yeah...they are interchangeable (mostly) It can be a regional It is based on location vs relative location to the speaker The only real clue I could find is that aca, as in this case, is more often associated with a verb. Please come here, Wait here etc... vs saying The food is here. We are here. Not a native speaker but that is my interpretation.