Prepayments
Welcome to the MYOB Community Forum, I hope you find plenty of useful information.
The first Question is where is the amount currently entered in your Opening Balances ?
When you created your file you should have entered opening balances from the Balance Sheet from the previous data file (Xero or whatever).
If you have not done this then your current file will be out of balance and you will end up with a large amount in Historical Balancing account.
You can fix this by
Going into your Chart of Accounts in the Liability area and create a new Account and call it NDIS Prepayments.
Make sure that you make this account a Credit Card type.
Once that is done you go back to the Menu Bar - Setup - Balances - Opening Balances and enter the amount against the new account. Make sure you remove the amount from whatever account is is currently in.
