you may go was flagged as incorrect.
In elementary school our teachers were dogmatic about using may for permission and can for ability.
If you would ask "Can I go to the bathroom?" they would invariably answer "I don't know. Can you?"
So how would I say "You may go". Seems to "Vi povas iri" would be the best translation. "Vi rajtas povi" seems too.... I don't know... tyranical or something. "You have the right to go."
If you want to dinstinguish between may and can in Esperanto, use rajti for may and kapabli or esti kapabla for can. But it's not mandatory: unlike your teachers, nobody will say you're wrong if you use povi for both may and can. PMEG says (originally in Esperanto, translated below. English is not my native language, so maybe there are some errors, but I think you'll understand :) ):
Povi shows an action or a state that's possible for the subject, whether because of the subject's capability, ability, strenght or power, or circumstances, right or permission. Only the context can show the precise meaning. [Original text: http://bertilow.com/pmeg/gramatiko/gravaj_verboj/povi_devi_voli/povi.html]
"can" is about ability, "may" is about permission or possibility
How about "Vi iros kun permeso."? or "Vi iras kun permeso." Or even better "You have permission to go." would that be "Vi havas permeso iri."?
"He may go, or he may not." "Li eble iros, aŭ li eble ne iros."