Purchases made online, by phone or through an app count as distance contracts in Türkiye, and distance contracts come with a right of withdrawal: within fourteen days of receiving the item you may withdraw from the contract without giving any reason and without paying a penalty.
In practice things usually stall at "your return request was rejected", "you pay the return shipping" or "your refund takes 30 days". Yet the deadlines and who bears the cost are set out plainly in the Distance Contracts Regulation.
This guide walks through how to send the withdrawal notice, how many days you have to ship the item back, which goods fall outside the right of withdrawal, and where to apply if the seller does not refund you.