Firstly, 'Till Buttons; will need to be configured to TOP-UP the account and SPEND money from the account.
To do this, click to Menu - Setup - Till - Till Button Tree. Double-click on 'Top Level' and choose 'Add'.
Create a Till Button called 'Account Top Up' (or similar) and choose 'Patient Account Top-Up' as its action. Then,
Create a Till Button called 'Account Spend' (or similar) and choose 'Patient Account Spend' as its action.