The default Z8 asset settings are for a margin account, not for a cash account. I would edit the AssetsZ8.csv and change the leverage everywhere to 1, since you have no leverage. After that, set the slider to the capital you want to invest.

Without editing AssetsZ8.csv, set the slider to half of the capital you want to invest, since the default leverage is 2. So with $5000 on the account, set the slider to 2250 when you want to invest 4500. The cash account won't give you a margin call (I hope), so a wrong slider setting is not fatal.