There are two types of balance that you cannot immediately withdraw - Free(ish) money and Frozen money.
You cannot withdraw Free(ish) money until you have made bets equal to its value. For example; if you earn €2.50 Free(ish) money, you cannot withdraw it until you bet at least €2.50. Bets made with your real money balance count.
You cannot withdraw Frozen money until you have ‘defrosted’ it by meeting the wagering requirements, see point 4 above for details on how this works.
If you have any questions on any of this please contact firstname.lastname@example.org