Ensure the following settings are applied:

site.properties

# Enables credit voucher display in the account
onlineuser.creditvoucher.disabled=false        
        

# Shows overall balance in the top right corner
customer.module.credit.balance.display.disabled=false  


# Enables top-up purchase option
customer.module.creditvoucher.topup.enabled=true 

customer properties

#enable buying credit vouchers in the customer portal
ONLINE_STORE_CREDIT_VOUCHER_DISABLED=false

#enable/disable the types as needed, the type general is always enabled
CREDIT_VOUCHER_TYPE_WEB_BOOKING_ENABLED=true
CREDIT_VOUCHER_TYPE_CLASS_REGISTRATION_ENABLED=true
CREDIT_VOUCHER_TYPE_WEB_PRIVATE_LESSON_BOOKING_ENABLED=true

#for NSW active kids voucher manual redeem (desktop contact extension)
# default is 'General" if not set
NSW_ACTIVE_KIDS_VOUCHER_TO_CREDIT_VOUCHER_TYPE=CLASS_REGISTRATION

See help page

https://help.sportlogic.com.au/knowledgebase/configuration-for-credit-voucher-purchase/