In the search bar, search for the customer > Click on his name > Click on "Adjust Balance".
Choose "Add" as adjustment type > Add the amount > Tick the box "No invoice created" > "Submit".
⚠️ Be careful: we don't keep track of this operation. Only to be used with caution. ⚠️
The client's account balance is now 20€. This amount could be used to bill him a new product (operation only available from the manager's side).
To create a negative account balance, follow the exact same process but select "Debit" as the adjustment type.