According to the blackmarket rule, posts about scams experienced outside of ePvP aren't allowed. This includes scams happening on Discord in this case.
The purpose of the blackmarket rule is to maintain a safe trading environment within ePvP. While your frustration is understandable, allowing posts about external scams wouldn't be effective in addressing them.
However, you might consider reporting the scammer to Discord directly. They have measures in place to deal with fraudulent activity.