Why not vous?
Would this be correct?: "Si vous êtes implolie, personne ne vous inviterez plus"
The subject of the second clause is personne (3rd person singular), therefore: Si vous êtes impoli, personne ne vous invitera plus.
why is malpoli rejected?
Why doesn't tu es become t'es the way te invitera becomes t'invitera
Because that's the rule of the language. Te contracts but tu doesn't. (In standard French, even though people sometimes contract tu in everyday speech.)
"Si tu es impolie plus personne ne t'invitera" rejected as of Apr 22,2021. Should be accepted. Reported.
I'm French and I agree with you. The translation of Duolingo is very clumsy and no used by French people.