If you want to exchange your gold jewelry, you first have to receive the money for your old jewelry from the jeweler, and then use that money to buy something new. Someone exchanged gold for gold and paid an additional €85 and was unaware of this. Is there expiation for her or what does she do now?

Ustadh AbdulAziz al-Haqqan

There is no expiation, and since she did not know the ruling there is no sin on her, in shā' Allah. She keeps the gold and avoids this in the future.