With respect to your closing query of being deemed 'sponsorship'...

With respect to your closing query of being deemed 'sponsorship' IMO it potentially allows FC Capital/Finstro to participate in the "Sales Commission" line in determining operating Cash flow and doesn't raise any red flags that there's off balance sheet debt liability being accrued here in the parent. If this was the case yes it is effectively effectively interest on a financing.

IMO the elephant in the room is if there was invoices being generated by BIG which some customers were not legally signed up to in an enforceable manner and those invoices were being upfront funded by FC Capital/Finstro. If this was the case the accrual of the GST will eventually catch up with them as GST is based upon invoiced revenues (only relevant to Australian SME customers).

IMO this is a little more complex than what BIG has thus far portrayed to the market and it will be interesting to see this all clarified in a detailed explanation of how the cash flow receipts are generated and how the cash flows through the business between reporting periods.