Same with Tugba; we are waiting for PayU integration in TURKEY detailed explanation about this issue can be found here https://ecommerce.shopify.com/c/payments-shipping-fulfilment/t/payu-turkey-payment-gateway-intregration-request-171263
Also many people requested the same payment gateway integration in TURKEY under this topic https://ecommerce.shopify.com/c/payments-shipping-fulfilment/t/payment-gateway-payu-integration-139825
Documentation for this integration can be found here: http://www.en.payu.com.tr/payu-payment-page