We generally allow only securities that are available for trading at IBKR to be transferred into the account.
To check if a security is available for trading, type in the stock symbol or ISIN into an empty Watchlist line of TWS and hit Enter. If available, a window will appear giving you an opportunity to load the symbol into the Watchlist and place a trade.
In case of bonds however, we could allow in certain cases to transfer in a position which is not available for trading and hold it till maturity.
Additional Information