Settlement is the behind-the-scenes process through which buys and sells for instruments are fulfilled.
Due to the complexities of this process, European orders typically settle after 3 working days of the trade date (T+3), which is the industry standard.
Once your order has been executed you’ve entered into a legal contract and your order will be fulfilled at the price displayed on your contract note.
If you execute a Sell order, the cash proceeds will appear in your available cash balance as 'unsettled cash'. This can be reinvested as soon as you’d like.
However, until the trade and resulting cash settles approximately 3 working days later, you can't withdraw it to your bank account. When the sale settles, the cash will no longer be 'unsettled cash' and instead will appear in-app as ‘withdrawable cash'. As this suggests, at this point you can trigger a withdrawal in-app if you want to.