The prepaid balance of a contact cannot be adjusted under CRM>contacts like with loyalty points, it must be done in the prepaid section.
To correct the prepaid balance of a contact:
Navigate to prepaid
Go to ‘Store’ and select ‘Prepaid’ from the dropdown menu.
Go to 'Transactions' and select 'add transaction'
Adjust the Point Balance
Find the contact with their email address with the search bar and select them from the results.
Select the shop to which this applies.
Enter the amount of value you would like to deduct in cents, ensuring to place a minus ‘-’ sign in front.
Complete the Transaction
Click ‘Create’ to complete the negative loyalty transaction.
The point balance of the contact has now been corrected.