Clarification on requirements to use trade system

Exactly what are the requirements to be able to use the trade system? I've found multiple answers, ranging from donate 10 USD to donate 10 EUR to donate "anything". Can anyone clarify, what are the requirements to be able to use the trade system, as of June 2018?

It's supposed to be any amount but last time I tried selling something from a premium account with 1 Euro donated, it didn't let me. So it might be 10 Euros or 10 USD if you have a donation method that shows amounts in USD.