Hey SM8ACE,
Appreciate the detail you’ve shared. The only reason I can think of for the liability account not showing up is that it might be a header account, which is used solely for reporting and account structure. Only detail accounts can have transactions recorded against them. Regarding the overpayment, you can record the full payment against the original invoice and let MYOB create a customer credit for the overpaid portion. Once that’s done, you can apply the credit to the next invoice or refund it to the customer (no need to juggle amounts into another account). Here’s a helpful link on how to handle customer overpayments.
Cheers,
Doreen