Why is the Trade Amount higher than expected when trading an option?

The order rejection "Error 503" message is displayed when your account does not have trading permissions for the product you are trying to trade.

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When you see the message "No opening trades: ineligible PINK stock" it means an opening order for that contract is not allowed, even if your account has trading permissions for US Penny Stocks.

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American style options can generally be exercised at any time prior to expiration, whereas European style options can be exercised only at expiration.

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Yes, you can short Bitcoin futures. Find more information on margin requirements on short Bitcoin Futures positions in the Trading Bitcoin Futures with IBKR article of the IBKR Knowledge Base. 

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