I have created a new customer, then entered the sales invoice details as shown, however the amount less GST appears in the Suspense account, not under Accounts Receiveable in the Summary window
Transactions are put in the Suspense account when there is an error in the data entry. You get them out of the Suspense account by correcting the error. Most easily found by drilling down on the suspense account and looking at the individual transaction. This is described in more detail in this guide Clear transactions in Suspense account