Also it might be because your funds were deposited less than 3 months ago. IB puts a 90-day hold on all funds deposited. Highway robbery, yes, I know.
Must be ACH and ACAT fraud preventative measures: https://www.csoonline.com/article/2...me-ach-fraud-why-criminals-love-this-con.html here's one from Robinhood customer
The 90-day hold would not be an effective measure against ACH fraud tbh. If somebody wants to commit ACH fraud, it can do it any time no matter how long is the hold. Considering this is a fraud that started to happen in 2009, more than 10 years ago and Robinhood, a brokerage that's just developed most recently wouldn't have any countermeasures put in place. Good thing IB has two-factor authentication for all withdraw and deposit requests.
My Balance available to withdraw is always a bit lower than actual liquidity. As i trade quite actively i guess this has to do with settlement, typically T+2.