Key Takeaways
Cash sits uninvested until you tell Amal where it goes.
Either way you land in the invest flow described in Invest, withdraw, rebalance.

Why is a few cents always left over?
Alpaca keeps a $0.01 buffer per order to satisfy regulatory rounding rules, so the maximum investable amount is slightly below the cash balance. The Cash available line in the invest dialog already accounts for this.

Deposit shows on Alpaca but not in Amal. Amal reads Alpaca's settled balance. Pending transfers are not investable yet. Refresh after Alpaca marks it complete.
"Insufficient funds" while some cash is shown. Part of the cash may already be assigned to an order that is still working. The cash card says "$X of this is being invested now" when that is the case.
I cannot see the Transfer out link. It is desktop only. On a phone use Transfers (Alpaca) from the More sheet.