Why did this happen?

This error signifies that the trading session or the instrument is under close-only mode. During this period, you are only allowed to close previously opened positions but not open new positions.

This can apply to instruments in close-only mode during high volatility periods or when the market is about to close. Note that sometimes instruments are placed in close-only mode before they are about to be delisted.

How to solve this error?

Stay up-to-date with what’s happening in the financial markets on the economic calendar, as well as the trading hours and holiday market hours. 

If the issue persists, open a ticket in the support hub for assistance.