Why is "А ти" incorrect? The English does not specify singular or plural "you".
It's correct just not accepted, don't forget to report
"Ти" is informal. If you cannot decide which form (formal or informal), always go with formal- "ви"
Я пенсіонер. а ти/ви?
would "ta vy" or "i vy" be acceptable or not in this context?
Does the dash matter between я and пенсіонер