I have already invested in the last three days: why doesn't my balance increase?
Upon receipt your funds are automatically invested (placed in a pool, usually within a few hours). But you won't see your interests (and therefore your balance) increase every day.
Your balance (including earned interests) is calculated/updated on the last day of each month at midnight (and not on a run-of-river basis) and expressed in EUR or USD. Your dashboard, therefore, does not show the interest earned in real-time but only at the end of the month (i.e., your "Current Balance" does not include "Direct Interest" and "Referral interests" of the current month).
You can nevertheless visualize your estimated earnings for the next 30 days on your dashboard based on the current performance.