Shein Customs Duty Now Paid Online? Unexpected Charge

I added about ₺970 worth of products to my cart on Shein. When I proceeded to checkout, I expected around ₺300 for shipping, but I was shocked when the total came out to ₺1900. Upon checking, I saw a customs duty charge of ₺580. I always thought customs duty was paid to PTT upon delivery, but it seems like it's now being charged online during the checkout process. Can someone please clarify if this is a new system? I’m confused and would appreciate more information on how this works. I wasn’t prepared for this extra charge, and it really impacted my purchase decision.