You can specify the GBP amount you want, not the number of shares. Whereas before you would have received an amount of whole shares and any surplus cash would be returned to your Freetrade ‘available to invest’ balance, now the cash amount that you reserve for a purchase will be used and you’ll receive a fractional amount of shares relative to that amount instead.
For example, if you wanted to buy £100 in a US stock, we’d execute an order for £100, and purchase a fractional amount of shares as close to that amount as possible.