New version 05/23 of Istanbul Kart for transport in Istanbul works fine, provided you can speak Turkish! I speak English, as do most tourists here. After spending time on English language info sites trying to decipher the kiosk button strokes to get a card at the Istanbul Kart machines, I had a local help me.
You need to use Turkish banknotes, 100 lira is best. Insert banknote. Card costs 50 lira, rest is 9.99 lira per transport ride = 5 rides. Insert card or hold on screen, wait for machine to (hopefully) scan the card, top up as needed (good luck) then tap card on turnstile to clear turnstile. Worked once for me, not again. Credit cards not accepted. Get card employee at airport to help you. No help anywhere else.
Worst machine interface I have ever used. Several other travelers complained about loosing their banknotes in the kart machine. No more Istanbul for me anytime soon, 3 mile walk from cruise port to Sultanahmet! Istanbul municipal government needs to join the 20th century and make their machines multilingual like the rest of the world, especially for a heavily visited site like Istanbul. Bon voyage Istanbul.