Price raised after buying an item?

Hi,

I am new to Vinted. I bought a pair of shoes three days ago and according to the chat the purchase went through. The seller contacted me today and told me that another person had offered higher than I had bought the shoes for and she would sell them to that person if I didn’t make a higher offer. She explained it in a way that if I was “still interested” in the shoes I could make a higher offer and then she would definitely sell them to me. It feels a bit strange to me so I wanted to ask if this was allowed and if not, where I can find information on this in the terms and conditions.

Thanks in advance :)

Edit: I just wanted to thank everyone for the advice and support :)