"Sir, work here, please."
Translation:Señor, trabaje aquí, por favor.
trabaje is also a command, as you are using "señor" trabaje is better here
Trabaja is the command form for tú, not usted. While I also tried trabaja, and was wrong, the explanation 'You used the command form "trabaja" instead of the él/ella/usted form "trabaje" ' is unclear at best. It would be much more helpful to say "You used the tú command form 'trabaja' instead of the usted subjunctive form 'trabaje'. (There is no command form for usted and ustedes, the subjunctive form is used.) The good news, I've learned something.
My correction for this same error simply said, "You used the wrong word."
According to Bescherelle, the imperatives of trabajar are:
2nd person singular: corta; 3rd person singular: corte
1st person plural: cortemos; (2nd person plural: cortad); 3rd person plural: corten