The most common cause of a negative cash balance is buying a security without sufficient cash in the local currency of that security.
Remember, Euro Pacific Trader does not allow you to “overdraw” your account in the traditional sense.
Instead, if you have Margin Trading enabled and you have available cash in other currencies, a margin loan will be created when you buy the foreign security, which is secured by your available currency.
In other words, your negative balance is being “collateralized” by other available cash or securities in your account.
This means you can buy securities in multiple markets and accrue negative balances (or “margin loans”) in those local currencies, and accrue negative interest as a result.