Hello. I fixed the problem. Now system should check if the product on PP end has appropriate data and if so, the payment will be processed.

But if I'm right you are using UNA 13. It means that your version of Payments module may have some other issues in PayPal API integration in comparizon with the newest one.

I have also search the internet, and came accross some people saying Paypal keeps its REST API cache and the only way to clear it is to delete your sanbox account. Well, I don't know if that information is accurate. But I am still searching about it.

I didn't hear naything about cache in REST API.