You may have opened non-base currency balances which limit the amount you can withdraw in a given currency. You may refer to the following link for instructions on how to convert these balances back to your base or other currencies: How can I convert currency?
If your account is a cash account and you recently executed a closing trade or currency conversion, you are required to wait for settlement before you can withdraw funds. This takes generally two (2) business days for stocks and for currencies (T+2).
If you recently deposited funds to your account, please be aware of withdrawal restrictions that might apply to your recent deposit.
If you have open the -F account UK Regulated used to trade CFDs, non-US index options and spot metals, you might have cash balances in such account that have to be transferred internally to the main account first. You can see cash balances in the -F account in TWS Account Window, section Market Value Real FX Balances, column "FX Cash"; you can also see these cash balances in your activity statements under the Cash Report section in the "UK Regulated" column. You can initiate an internal transfer by logging in to Client Portal and selecting the menu Transfer & Pay followed by Transfer Funds. Click on the account number in the upper part of the page and select the account ending in F. Then pick Internal Transfer and select Full Transfer in the Currency drop-down. Click Continue, confirm by entering username, password and the code sent to your email and click Continue. The transfer will be reflected on the account instantaneously.
Please Note
As part of its anti-money laundering efforts, IBKR implements restrictions on certain client deposits and withdrawals. Find out more about Funds Transfer Restrictions in the IBKR Knowledge Base.
Additional Information
How can I check my cash balances in the Activity Statement?
Are there any limits to the amount I can withdraw?
What determines how much cash is Available for Withdrawal in a Margin account?
What determines how much cash is Available for Withdrawal in a Cash account?